Important Note About Stalling

Car stalling repairs, especially Chrysler, Dodge, and Plymouth

We have generally found most stalling issues come from one of the following areas, on fuel injected cars. (We do recommend reading this whole page, and strongly recommend first checking for computer error codes).

We would like to note that Chrysler products have a tendency to have failures in relatively inexpensive-to-fix areas, and that mechanics have a tendency to replace large, expensive parts when this happens. How many 1970s cars got new electronic ignitions systems when the $3 ballast resistor failed? How many got new engines and transmissions, or were crushed into cubes, because of ten cents worth of bad vacuum hose?

We hope this page will continue to save people from careless dealers and mechanics, and point them to relatively inexpensive parts that they can replace themselves in less time than it takes to get a ride back from the dealer.

• Burglar alarms - probably the most common problem now. Often mis-diagnosed ... example (the symptoms often vary): I have a 96 Dodge Intrepid and it would start then just shut off... The lights would strobe and there was a ticking noise coming from somewhere around the fuse panel (inside the car)... Almost cost me $300 for a new fuel pump as that is what I was told was the "most likely culprit"... Turned out to be the security and a simple lock and unlocking of the door a few times totally fixed the problem... (Terra Sears)
• The Hall Effect sensor - this can fail and not set an error code. However, if the computer gets no data from the Hall Effect sensor, it will assume that the engine is not turning, and will not provide any fuel. This is an inexpensive gadget that sits underneath the rotor, in the distributor cap, on cars without distributorless ignition (so this doesn't apply to cars made after about 1996). A good first step and not hard to replace, even for beginners.
  • In Steve Meade's case, in cold weather, the engine would run for about a minute, then die - each time it was started. Using the gas worked to keep it running until it ran warm. There were no codes set. In his case, he needed a new pickup rotor - part of the distributor ($113).
  • The Auto Shutdown Relay (ASD) - actually, this rarely breaks, but when it does, the engine stays off. One purpose of the auto shutdown relay is to avoid "dieselling." It kills all fuel delivery and spark. The ASD can be triggered by a broken wire or short in another place -e.g. the fuel pump.
  • The MAP sensor - another frequent cause of stalling or non-starting. This measures the air pressure in the manifold. It is usually mounted on a fender, costs around $25, and is easy to replace. You can test it - if your car won't start, just unplug the electrical connection from the MAP sensor. If it starts, replace the sensor. MAP sensor details. (It may act as though the fuel pump is not working properly - starting, then quickly dying).
  • There is a relay between the computer (PCM) and coil, at least on the 2.2/2.5 TBI, that costs about $12. If it fails, mechanics may try replacing the computer (thanks, Ronald Knauf).
  • ...and, of course, the starter relay - often this goes and it is misdiagnosed as the starter itself, the computer, etc. (thanks again, Ronald Knauf).
  • Fusible links: John Auto Tech wrote, "try checking the fuseable links located by the drivers side strut tower. Give each one a [gentle] tug to see if one stretches like a rubber band."
  • Loose or dirty computer or battery connections - surprisingly common! Or (on vintage cars) check the hot wire going into the firewall plug... on the other side the wire goes to the fuse box then to the dash- when it goes to the dash it goes to the alt meter... it is a simple fix and one that should be checked. (It is also a good place for a fire - you've got loose hot wires and lots of loose insulation)
  • The idle speed motor - this can, for example, cause stalling when the engine is cold, but not when hot. If you replace the idle air control motor (IAC), also clean the throttle body and reset the computer (you can just disconnect the battery for a few minutes). This problem can also affect newer cars such as the Neon which have no distributor.
  • Plugged exhaust (e.g. catalytic converter). F.J. MacFarlane wrote about this, noting that most or all US 2.2 carburted engines had two converters in series.
  • Clogged fuel filter or fuel line - this can be under the hood or in the tank. Similar symptoms can be caused by a weak fuel pump. There are, incidentally, two types of fuel pressure test: one which tests an instant of pressure, and a more sustained test. The latter can often solve stumble and stall problems that occur at highway speeds or under acceleration.
  • The speed (distance) sensor - see Ed Hennessy's notes below.
  • Spark plug wires - Rosegate noted that a problem with missing cylinders was resolved by changing the wires. A dealer failed to solve the problem, charging $130 apparently to change a single wire. You can do this yourself in ten minutes; you can get very high quality wires for $40 (four cylinders).
  • The oxygen sensor - somewhat expensive to replace (they cost about $40-60 just for the part), but since the oxygen sensor is the thing that tells the engine whether it's feeding too much or too little fuel, it's pretty important. The oxygen sensor can be damaged by bad gas or excess pollution from another bad sensor or part. Bad oxygen sensors can cause high idling, rough idling, stalling, lack of power, and poor fuel economy, not to mention excessive pollution. "An O2 sensor actually generates voltage and when active, varies between .5 and 1.0 V. which is rich/lean. It's working ok if you see a wave between these numbers. If you see one steady reading the sensor is likely bad. Don't forget the sensor must be hot to stard working." - Wayne Moschella
  • Fuel line cracks - it happens, and they can be hard to find. Turbo engines should be periodically and carefully inspected for leaking fuel lines, due to their higher fuel pressures. Small, hard to see fuel line cracks can cause stalling and non-starting. Check not just the main fuel line but also delivery lines that feed individual injectors (thanks, R. Jake Carr).
  • Low fuel pressure - applies only to 1988-90 models (see below).
  • Jim Zellmer wrote: a rubber elbow coming out of the rear intake manifold [may have a] crack that is not readily visible from the front of the car. The crack would open an cause a vaccuum leak big enough to shut down the engine.

For non-fuel injected cars, most stalling issues can be traced to the carburetor or timing settings. A good tune-up with high quality wires, rotor, and distributor cap can often permanently solve stalling. For other ideas, visit Valiant Varieties.

Notes on dealing with bad sensors

Dirt and water can get between any sensor and the wire leading back to the computer, so first check the contacts for each sensor. Sometimes, you can buy a "splice kit" which replaces just the part of the wire near the sensor. If it means not buying a full harness, you can also make a temporary fix by buying the end of the wire from a junkyard and splicing it on. It is safest to only buy genuine Mopar / Chrysler parts, especially with the oxygen sensor. Intex Axecat noted that his Hall Effect sensor was soaked in oil - replacing the cheap O-ring on the distributor base fixed it.

Other possible stalling solutions

from Vern

In the 1987 Plymouth Reliant and, likely, other cars of the era, there is a hidden connector in the power lead to the power module. From the top connector, closest to the fire wall, there is a red lead. Unwrap the binding tape from the wire bundle about 6 inches to expose an inline crimp connector (a factory kludge) which may be corroded and intermittent.

from pckolb

If you have a van that stalls with a fuel problem, try removing the valve on the passenger end of the front fuel rail, the one with the vacuum hose to it, let the fuel run out and flush the valve and then reinstall it. I did that with my 1990 Caravan and it hasn't stalled since. (Warning: Whenever you deal with gasoline, obey all safety precautions, e.g. first relieve fuel line pressure, do not smoke, avoid sparks, etc. Proceed at your own risk.)

from Erik Namtvedt

You should add a section about losing all electrical power to the entire car: this happened to me and with the 1968 Charger RT the problem is with either the ground strap for the battery etc... or check the hot wire going into the firewall plug... on the other side the wire goes to the fuse box then to the dash- when it goes to the dash it goes to the alt meter... here is where my weak link was.... it is a simple fix and one that should be checked. (It is also a good place for a fire- you've got loose hot wires and lots of loose insulation)

from Daryl Koehl

(3.3 V6 engine) You cannot see the problem until you actually remove the flywheel because there is a small plate that goes under the bolts that hides the problem. With the plate and flywheel removed you can see that the flywheel has sheared a complete circle around the entire set of bolts. You must remove the flywheel to see this. The effect of this shearing is that the engine timing (which is generated from the slots on the flywheel) is totally random and dynamic.

From Andrew N.

The vehicle is an 1988 Dodge Aries 2.2. I was having issues with the car stalling in hot weather when I would come to a stop sign or trafic light. The fuel pump was replaced but then it would start and run for about 2 to 4 seconds then stall. The auto shutdown relay was replaced with no change. A good supply of fuel was being delivered, and the return line at the throttle body had pressure; but at the gas tank there was just a trickle coming from the return line. A section of line was removed and a blockage blown out of the line. It would appear if the pressure on the return line is too great, the engine will automatically turn off. The old pump still allowed the engine to run as it was not sending enough pressure to cause the shut down.

from Ed Hennessy

(In response to someone whose Aries coughed, sputtered, and died sometimes when coming up to a stop sign - and sometimes recovered to a smooth idle. No computer codes were set.)

This is a classic symptom of a dead speed-distance sensor. The hall effect tends to fail only when hot and doesn't usually matter if you stop or not. It won't start that easily again until it cools. A bad speed sensor will stall the engine, but it will always fire right up immediately.

What happens with a bad speed sensor is that the computer can no longer tell that the car is moving or not, so it can't tell when to open the AIS motor so the motor will idle when you stop. So the engine spits, and sometimes the computer can catch it.

I have done 3 ('87 LeBaron K 2.5, '86 Reliant 2.5, '91 Acclaim 2.5) and none have ever set a code. Apparently, the signal was in range for the computer (so no code) but completely inappropriate for conditions. All three cars had the same symptoms as yours. The LeBaron was mine, and it had a digital dash. The digital speedo had erratic readouts as well.

You can check the sensor with an ohmmeter. Pull the sensor, and then connect the probes to the two terminals. You should see 8 pulses of zero resistance with infinite resistance in between. Anything else, and the sensor is bad. The LeBaron's had 8 zero pulses, with relatively high (but not infinite) resistance in between.

From Victor Coutu

(1986 2.2L Canadian Dodge Aries.) My car would abruptly die for no obvious reason. Didn't matter if I was stopped, idling, accellerating or slowing. And it would be difficult to start afterwards, ie: cranking but not firing.

I had already replaced the O2 sensor (which was bad), plugs and wires. The fuel filter was new, and the 'Hall Effect' had been replaced by the previous owner in October of '99. I replaced the gas tank and the fuel pump as part of the requirements for a 'fitness' when I bought the car shortly afterwards. When the car ran, it ran like a song.

I had the car scoped, and it wasn't throwing any codes, even though it stalled during the test. We were all baffled, until another mechanic wandered by and poked his head in. He noticed 'wetness' on the fender below the ignition coil, and suggested the coil might be leaking, resulting in an intermittent short.

We pulled it, and discovered it was damp and rotten, but saw no holes and no new seepage after wiping it down. I bought a new one anyway, and took the car home to install it. When I started to remove the coil, I found a huge amount of fluid running down the underside of the 'can'. The clamp apparently had contributed to the problem, by 'squishing' the 'can' enough that it separated from its 'lid'. This was why it didn't leak while it was out of the clamp at the garage. I replaced it, and am pleased to say that the problem has disappeared.

Low fuel pressure (Artie M.)

This stalling problem is very common on all 1988-1990 2.2 liter engines with automatic transmission and air conditioning. It was resolved in 1991 when the computer was redesigned and the fuel pressure was increased. We had both an 88 and an 89 Sundance. Both had this problem.

The car idles normally when in drive, but not when the a/c compressor is on. Putting the car in neutral when idling with the a/c on solves the problem, but is very annoying. The problem starts between 50-60k miles and gets worse. Changing the parts suggested is previous responses won't work.

For some reason (I never could find out why) the automatic idle speed motor runs out of adjustment range (motor wear? tranny wear? a/c wear?) We solved the problem using two not very elegant fixes. On one car we jury rigged an old a/c solonoid (the type used on cars w/carburetors). It was a pain to hook up but it did work, opening up the trottle plate about a sixteenth of an inch when the compressor engaged. On the other car, we adjusted (which you are not supposed to do) the throttle plate adjusting screw about 1 1/2 to 2 turns clockwise which was easy to do. The car idled OK in drive with the a/c on, except in very hot weather (when the compressor had to put out higher pressures). The downside was that with the tranny in park and the a/c off, the motor idled at about 900 rpm.

We never had any problems with either car, both got over 30mpg on the highway and had about 150,000 miles on them when we got rid of them. The only non-maintenance items we relaced were 2 map sensors on each car, and a radiator on one.

Stalling in wet weather

Try replacing the wires and making sure they are all tight, and spray with silicone spray all wires related to the ignition under the hood (including the electronic ignition wires - not the ignition brain itself, and watch to avoid getting the silicone into the connectors.) You can also check to make sure the wiring harnesses are seated properly. I think Chrysler recommends taking 'em out, cleaning them, spraying them wtih a special white grease - not ordinary lithium grease - and putting 'em back in again. Also check and clean the battery cables where they attach to the posts!

Dakota cold stalling

My '91 Dodge Dakota started giving me drivability problems - meaning it would die out when cold, then restart when I shut off the key and restarted. Allpar led me in the right directions to troubleshoot the components that feed the engine computer, and I finally decided it had to be changed. One long-standing problem had been a bad voltage regulator (part of the computer) which I had "wired around" with the regulator out of an '89 diesel model, so I replaced the engine computer and removed the external regulator.

The engine computer comes in two versions, california spec and other-49. my truck started life as a california spec, but I don't live in california, so decided to try to save a hundred bucks by getting the other-49 computer and see what would happen. Everybody told me it would never work, the engine would either not run or self-destruct. What a surprise! Starts better, runs smoother, has more initial pickup than ever before! will have to see what the long-term fuel economy change is, but I am really glad I did this!

From jerry rogich: fuse block

My 1993 Dakota 5.2L would buck, stall and sometimes not start. I had a 42 error (ASD) /51/52 and found the ASD relay was ok but the voltage was disappear. Found that under the fuse block, inside the harness there is a junction of 3 green wires that had oxidized and was intermittent. Fixed this and everything was ok.

MAP sensor note

Jim Siperek wrote: There was a tech bulletin for this that suggested a MAP sensor valve kit (basically a vacuum tee, a short piece of vacuum hose and a vacuum valve) that cures the problem of failing MAP sensors. My '87 Reliant wagon ate 3 MAP sensors in less than a year (2 vacuum failures & an electrical failure) until a dealer told me about this kit. Try talking to your local CPDJ dealer and have them look this up for you. It never failed again after I installed it.

Bad pump ("seatiger")

Found that my 1987 Dodge Shadow ES began stalling when idling and turned the steering wheel. The hydraulic steering pump is almost dead. Disconnected the belt pump and the car run smooth and without rough idling.

Water in the sensors

“I have a 1993 Chrysler Town & Country minivan - 3.3L V6, 160,000 miles - that would momentarily cut out - sometimes for just a split second, and sometimes for several seconds. Didn't matter whether I was accelerating, cruising, slowing, or idling. Looked everywhere online trying to find a similar problem. PepBoys and the dealer said either the CRANKSHAFT or CAMSHAFT position sensors were the most likely culprits. Read online somewhere that these sensors don't like rainy weather, and can act up from such. All I did was crawl underneath, found the crankshaft sensor, wiggled it around a little, and that fixed the problem!!!! (Might try unplugging and plugging it back in too).
Felt like I should post this since I haven't seen much about these two important sensors (my van has distributorless ignition, so it doesn't have hall-effect).”

From Jay Smith

A number of years ago my 1989 Ramcharger would start and then immediately stall. I could let it sit from anywhere between 1-12 hours before it would start and stay running. After a total of 3 days over a one month period, a dealership was unable to locate the problem. One day I started going though everthing... as I was laying under the truck, I noticed that the gas tank was deformed (plastic tank)... the whole center of the tank was bowed upward! I reached around the side to the gas cap and as I loosened the cap, I could here air being pulled into the tank and the center of the tank fell back to where it should have been. I'm assuming that when I had a low fuel level, the valving in the gas cap wasn't letting fresh air into the tank; as fuel went out while driving, a vacuum was created and the center of the tank would pull up and interfere with the fuel pickup. If the truck sit long enough, enough air would bleed back into the tank to stop the interfence. I took the cap apart and cleaned it but it happened again so I just drilled a very small hole through the cap and haven't had a problem in 14 years. [Allpar would recommend buying a new cap to avoid unnecessary evaporative emissions.]

Bohdan Bodnar's troubleshooting: 2 examples

Stall at low rpm

I have been having problems with my 1987 Horizon. When I go to take off, it wants to die. The only way that I can get it to take off is to take the rpm's up to about 6000. When I speed up, it will hop. When it does this the tach. will also hop or jump around.

The distributor pickup will not cause these types of problems -- it will cause the engine to either cut out or cut in. I don't know whether this is a fuel injected engine or not so some of the following comments may not be applicable; I also don't recall whether this car has an automatic transmission or not:

Fuel injected with automatic transmission.

Pull diagnostic trouble codes. After the "55" has been flashed, move the transmission gear selector from Park to Neutral to Reverse/Drive. The power loss light should flash indicating that the computer is seeing changes in the neutral safety switch. If no changes are seen, the engine may bog when switching gears because the idle anticipation will not work. Injector base pulse width is also partially controlled by this switch.

Fuel injected.

Check to ensure that there are no TPS related diagnostic trouble codes (DTCs). In an EFI engine, the TPS serves as an "electronic" accelerator pump. If the TPS circuit is not operating, the computer will not be able to react to sudden changes in throttle setting.

Check fuel pressure against factory specs. If this is TBI, pressure should be 14.5 psi +/- 1 psi.

All engines.

The symptoms you've described appear to be "trailer hitching." This is often traced to the ignition system malfunctioning. My recommendation is that you measure the resistance of the ignition wires and replace any which exceed roughly 15k ohms (you can operate substantially above factory specs IF the rest of the ignition system is in pristine condition -- like in my 1986 Le Baron). If the rotor appears to be worn, replace rotor AND cap. Check the resistance of the ignition coil -- primary should be about 1.5 ohms whereas secondary will be a few kilo-ohms. If you have access to a conventional oscilloscope, scope the primary side of the ignition coil; the pulse width (burn time) should be between 0.85 ms and about 2 ms (my Le Baron has between 1.9 and 2.1 ms). Also, the pulse during the burn time should BE FLAT. If it's tilting upward, then you have either excessive circuit resistance or lean misfire. The firing voltage (spike) should be around 200 volts; if it's substantially less than that, then either you have a short someplace in the secondary ignition system or the primary has excessive resistance. If you have an EFI engine, measure the voltage from the + side of the ignition coil to ground -- it should be within a few hundred millivolts of battery voltage (the positive side also goes to the fuel pump -- the entire circuit is fed by the ASD relay in the computer/power module). Check sparkplugs -- gap on the Champion RN12YC sparkplugs is 0.035" (THIS I know by heart!).

Clean the coolant temperature sensor connections with television tuner cleaner -- these will often corrode and cause the computer to see an abnormally low temperature (and thus flood the engine).

Carbureted engine

Assuming you've done all the above, connect a high impedance dwell meter to the mixture control solenoid. Set the meter for the 6 cylinders scale. With the engine in closed loop, the average dwell should be 30 degrees (50% duty cycle on the m/c solenoid). See the FAQ for further details.

Immediate stall

It starts, then immediately stalls, warm or cold...like the bottom falls out. About a month ago I had it diagnosed and replaced the SMEC (computer). It seemed to fix it until Wednesday, when I had the battery replaced. Same problem again. Start, stall, start stall. I replaced the oxygen sendor, the EGR, temp sensor, took off the throttle body and cleaned it with gumout spray. It seems to run better for a while after fuel injector cleaning. A new fuel pump was installed about 4 months ago with a new filter. 14.5PSI and the DBI reads the AIS is OK.

Bohdan Bodnar wrote: I think a lot of stuff was blindly replaced without thinking things through. If this was my car, here's what I'd do:

On a cold engine, read the coolant temperature sensor output and see if it agrees with the ambient temperature. On my 1986 Le Baron, the measured temperature and ambient agree to within about 2 degrees F (sometimes, the agreement's even better). If you don't have a scan tool, take a reading with a high-impedance voltmeter and send me the voltage reading -- I have a table of temperature vs. voltage for all EFI Chrysler products through 1992 (1993?).

Measure the resistance of the secondary side of the ignition coil to one of the primary terminals. It should be (working from memory here) around 8k ohms. If it's more than about 12k, replace the coil. Primary side resistance should be around 1.3 ohms (from memory). If it's above 2 ohms or below about 1 ohm, replace the coil. If you have specs, use THEM, not me -- I haven't measured the resistance on one of these coils for over a year.

Stick a high impedance voltmeter from the switched battery feed on the ignition coil to ground and put the ignition key in run. For about two seconds, you'll read something very close to battery voltage -- the difference should be < 500 mV. The positive side of the ignition coil is electrically connected to the fuel pump; this circuit is driven off of the autoshutdown relay inside the SMEC (Power Module, in my case).

Measure the resistance of the fuel injector + throttle body harness. It should be around 1.2 ohms. Resistance specs for this injector vary year-to-year. In general, the resistance is around 1 to 1.5 ohms. The harness introduces around 0.3 ohm extra resistance.

What is the condition of the spark plugs? This engine takes Champion RN12YC with 0.035" gap.

Measure the resistance of the ignition wires. Each wire should be, at most, around 10k ohms (Chrysler's specs are lower than this, but I don't have the pertinent information available). If any wire's significantly higher than this, replace it. Is the cap and rotor ok?

Connect a high-impedance voltmeter to the red wire on the MAP sensor and put the car in "run" (engine off). You should read 5.0 volts. Now, read the signal return voltage -- it should be around 4.9 volts (green wire, probably). Connect a vacuum pump to the MAP sensor and pump up a vacuum. The voltage should fall. If it doesn't, replace the sensor. Examine the vacuum hose which you just disconnected; does it have a silicone gel visible? If so, then the MAP sensor's falling apart internally. Check the hose going from the MAP sensor to the vacuum source for integrity.

My intuition is that this is an ignition problem. On a cranking engine, the a/f mixture is very rich and therefore easy to ignite. Once you start the engine, the computer will lean the a/f mixture. Your fuel pressure looks perfect (if the return hose was clogged, the pressure would be MUCH higher. Is the fuel system intact? With the fuel pressure gauge connected to the intake side, put the ignition key in "run" (engine off). The computer will turn on the fuel pump for about 2 seconds and pulse the injector. The fuel pressure should be stable for several minutes. If it drops quickly, then something's leaking (injector, regulator, or bad check valve in the pump).

New "immediate stall" repair

I had this exact problem with my 1989 Caravan (2.5L TBI engine). The van was running fine then started acting like I would expect if the fuel pump were about to die. Within a couple days it had progressed to a start then immediate stall condition exactly as described [above]. Here's what's going on (or at least in my case).

There appear to be two controls for the injector, one which fires the injector during startup and another (the main ECM) which takes over controlling the injector approximately 1 sec after start. The start circuit seems to have have much more current behind it than the ECM running feed. (I suspect to allow starting with a low battery where the ECM may not get sufficient voltage during cranking) .

When the plunger in the injector is sticking due to varnish build up, this start signal is able to operate the injector while the running feed from the ECM doesn't have enough current (injector function is an electromagnet - more current=more pull on the internal plunger). It would start, but immediately stall every time. In my case I removed the injector from the car and backflushed it with cleaner. Problem solved.

Since my method of backflushing the injector is probably a bit technical for the average DIY (involving a modified 9v power supply to pulse the injector at 60hz, hose and a hand pump), it may be advisable to recommend people simply replace the injector, especially considering the average person may not understand the cleanliness factor while doing this as any dust or grit accidently flushed up through the bottom of the injector could ruin it anyway, resulting in another misdiagnosis when they reinstall a stuck injector thinking it is now "good".

Engine Coolant Sensors

Copyright AA1Car

The engine coolant temperature (ECT) sensor is a relatively simple sensor that monitors the internal temperature of the engine. Coolant inside the engine block and cylinder head(s) absorbs heat from the cylinders when the engine is running. The coolant sensor detects the change in temperature and signals the Powertrain Control Module (PCM) so it can tell if the engine is cold, warming up, at normal operating temperature or overheating.

The coolant sensor is extremely important because the sensor's input to the PCM affects the operating strategy of the entire engine management system. That's why the coolant sensor is often called the "master" sensor.

Many of the fuel, ignition, emissions and drivetrain functions handled by the PCM are affected by the engine's operating temperature. A different operating strategy is used when the engine is cold than when it is warm. This is done to improve cold driveability, idle quality and emissions. Consequently, if the coolant sensor fails or is giving the PCM a false reading, it can upset a lot of things.

HOW THE COOLANT SENSOR AFFECTS ENGINE OPERATION

Input from the coolant sensor may be used by the PCM for any or all of the following control functions:

* Start up fuel enrichment on fuel injected engines. When the PCM receives a cold signal from the coolant sensor, it increases injector pulse width (on time) to create a richer fuel mixture. This improves idle quality and prevents hesitation while the cold engine is warming up. As the engine approaches normal operating temperature, the PCM leans out the fuel mixture to reduce emissions and fuel consumption. A faulty coolant sensor that always reads cold may cause the fuel control system to run rich, pollute and waste fuel. A coolant sensor that always reads hot may cause cold driveability problems such as stalling, hesitation and rough idle.

* Spark advance and retard. Spark advance is often limited for emission purposes until the engine reaches normal operating temperature. This also affects engine performance and fuel economy.

* Exhaust gas recirculation (EGR) during warm-up. The PCM will not allow the EGR valve to open until the engine has warmed up to improve driveability. If EGR is allowed while the engine is still cold, it may cause a rough idle, stalling and/or hesitation.

* Evaporative emissions control canister purge. Fuel vapors stored in the charcoal canister are not purged until the engine is warm to prevent driveability problems.

* Open/closed loop feedback control of the air/fuel mixture. The PCM may ignore the oxygen sensor rich/lean feedback signal until the coolant reaches a certain temperature. While the engine is cold, the PCM will remain in "open loop" and keep the fuel mixture rich to improve idle quality and cold driveability. If the PCM fails to go into "closed loop" once the engine is warm, the fuel mixture will be too rich causing the engine to pollute and waste gas. This condition may also lead to spark plug fouling.

* Idle speed during warm-up. The PCM will usually increase idle speed when a cold engine is first started to prevent stalling and improve idle quality.

* Transmission torque converter clutch lockup during warm-up. The PCM may not lockup up the torque converter until the engine has warmed up to improve cold driveability.

* Operation of the electric cooling fan. The PCM will cycle the cooling fan on and off to regulate engine cooling using input from the coolant sensor. This job is extremely important to prevent engine overheating. Note: On some vehicles, a second coolant sensor or switch may be used for the cooling fan circuit only.

TYPES OF COOLANT SENSORS

Most coolant sensors are "thermistors" that change resistance as the temperature of the coolant changes. Most are the "NTC" (Negative Temperature Coefficient) type where resistance drops as the temperature goes up. With this type of sensor, resistance is high when the engine is cold. As the engine warms up, the internal resistance of the sensor drops until it reaches a minimum value when the engine is at normal operating temperature.

A typical GM coolant sensor, for example, may have around 10,000 ohms resistance at 32 degrees F and drop to under 200 ohms when the engine is hot (200 degrees). A Ford coolant sensor, by comparison, may read 95,000 ohms at 32 degrees and drop to 2,300 ohms at 200 degrees.

Resistance specifications will vary depending on the application, so any sensor that does not read within its specified range should be replaced.

Coolant sensors have two wires (input and return). A 5-volt reference voltage signal is sent from the PCM to the sensor. The amount of resistance in the sensor reduces the voltage signal that then returns to the PCM. The PCM then calculates coolant temperature based on the voltage value of the return signal. This number can be displayed on a scan tool, and may also be used by the instrument panel cluster or driver information center to display the temperature reading of the coolant.

On some applications, a "dual range" coolant temperature sensor may be used. When the coolant reaches a certain temperature, the PCM changes the reference voltage to the sensor so it can read the coolant temperature with higher accuracy (higher resolution).

On some older vehicles, a different type of coolant sensor may be used. Some of these are essentially an on/off switch that opens or closes at a predetermined temperature. The sensor may be wired directly to a relay to turn the electric cooling fan on and off, or it may send a signal to a warning light on the instrument panel. These older coolant sensors are typically single wire sensors. On other older applications, a single wire variable resistor temperature sensor that grounds through the threads may be used to send a temperature signal to a gauge on the instrument panel. These are typically called temperature "senders" rather than sensors.

FINDING THE COOLANT SENSOR

The coolant sensor is typically located near the thermostat housing in the intake manifold. On a few vehicles, the coolant sensor may be located in the cylinder head, or there may be two coolant sensors (one for each cylinder bank in a V6 or V8 engine) or one for the PCM and a second for the cooling fan.

The sensor is positioned so the tip will be in direct contact with the coolant. This is essential to produce a reliable signal. If the coolant level is low, it may prevent the coolant sensor from reading accurately.

COOLANT SENSOR SYMPTOMS

Because of the coolant sensor's central role in triggering so many engine functions, a faulty sensor (or sensor circuit) will often cause cold driveability and emission problems. A bad coolant sensor can also cause a noticeable increase in fuel consumption, and it may cause a vehicle to fail an emissions test if it prevents the engine management system from going into closed loop.

Keep in mind that many coolant sensor problems are more often due to wiring faults and loose or corroded connectors than failure of the sensor itself.

The coolant sensor's impact on the engine management system, cold driveability, emissions and fuel economy can also be influenced by the thermostat. If the thermostat is stuck open, the engine will be slow to warm up and the coolant sensor will read low. Or, if someone installed the wrong thermostat for the application or removed the thermostat altogether, it will prevent the engine from reaching normal operating temperature and cause the coolant sensor to read low.

COOLANT SENSOR DIAGNOSTIC FAULT CODES

On 1996 and newer vehicles with OBD II onboard diagnostic systems, a faulty coolant sensor may prevent some of the system monitors from running. This will prevent the vehicle from passing an OBD II emissions test because the test can't be done unless all the required system monitors have run and passed.

The OBD II system should catch the fault, turn on the Check Engine Light or Malfunction Indicator Lamp (MIL), and set one of the following diagnostic trouble codes:

P0115....Engine Coolant Temperature Circuit
P0116....Engine Coolant Temperature Circuit Range/Performance
P0117....Engine Coolant Temperature Circuit Low Input
P0118....Engine Coolant Temperature Circuit High Input
P0119....Engine Coolant Temperature Circuit Intermittent 

On older pre-OBD II vehicles, the Check Engine light may come on if the coolant sensor is shorted, open or is reading out of range. GM coolant sensor codes include codes 14 & 15, Ford codes are 21, 51 & 81, and Chrysler codes are 17 & 22.

COOLANT SENSOR DIAGNOSIS

A visual inspection of the coolant sensor will sometimes reveal a problem such as severe corrosion around the terminal, a crack in the sensor, or coolant leaks around the sensor. But in most cases, the only way to know if the coolant sensor is good or bad is to measure its resistance and voltage readings.

On vehicle systems that provide direct access to sensor data with a scan tool, the coolant sensor's output can usually be displayed in degrees Centigrade (C) or Fahrenheit (F). The coolant sensor should read low (or ambient temperature) when the engine is cold, and high (around 200 degrees) when the engine is hot. No change in the reading or a reading that obviously does not match engine temperature would indicate a faulty sensor or a wiring problem.

The internal resistance of a coolant sensor can also be checked with an ohmmeter or DVOM (digital volt ohm meter) and compared to specifications. If the sensor is open, shorted or reads out of range, it must be replaced.

If the resistance of a coolant sensor is within specifications and changes as engine temperature changes, but the engine is not going into closed loop, the fault is in the wiring or PCM. Further diagnosis will be needed to isolate the problem before any parts are replaced.

One trick here is to use a sensor simulator tool to feed a simulated temperature reading through the sensor's wiring harness to the PCM. If the wiring continuity is good but the PCM fails to go into closed loop when you send it a "hot coolant" signal, the problem is in the PCM.

COOLANT SENSOR VOLTAGE CHECKS

You can also use a voltmeter or digital storage oscilloscope (DSO) to check the sensor's output. Specs vary, but generally a cold coolant sensor will read somewhere around 3 volts. As the engine warms up and reaches operating temperature, the voltage drop should gradually decrease down to about 1.2 to 0.5 volts. If you're using a scope to display the voltage signal, you should get a trace that gradually slopes from 3 volts down to 1.2 to 0.5 volts in three to five minutes (or however long it normally takes the engine to reach normal operating temperature).

If the voltage drop across the coolant sensor reads at or near 5 volts, it means the sensor is open or it has lost its ground connection. If the voltage is close to zero, the sensor is shorted or it has lost its reference voltage.

When working on 1985 and up Chrysler products, watch out for a sudden voltage increase as the engine warms up. This is normal and is produced by a 1000 ohm resistor that switches into the coolant sensor circuit when the sensor's voltage drops to about 1.25 volts. This causes the voltage to jump back up to about 3.7 volts, where it again continues to drop until it reaches a fully warmed up value of about 2.0 volts.

Sometimes a coolant sensor will suddenly go open or short when it reaches a certain temperature. If your voltmeter has a "minimum/maximum" function, you can catch sudden voltage fluctuations while the sensor is warming up. If you are viewing the voltage pattern on a scope, a short will appear as a sudden drop or dip in the trace to zero volts. An open would make the trace jump up to the VRef voltage line (5 volts).

If the coolant sensor reads normally when cold (high resistance and 3 or more volts), but never seems to reach normal temperature it could be telling the truth! An open thermostat or the wrong thermostat may be preventing the coolant from reaching its normal operating temperature.

COOLANT SENSOR REPLACEMENT

Most coolant sensors are not replaced unless they have failed. A coolant sensor that is shorted, open or reading out of range obviously can't provide a reliable temperature signal and must be replaced for the engine management system to function properly. But many experts also recommend installing a new coolant sensor if you are replacing or rebuilding an engine. Why? Because coolant sensors can deteriorate with age and may not read as accurately as they did when they were new. Installing a new sensor can eliminate a lot of potential problems down the road.

It is also a good idea to replace the coolant sensor and thermostat if the engine has experienced a case of severe overheating. Abnormally high engine temperatures can damage these components and may cause them to misbehave or fail prematurely.

Replacing a coolant sensor requires draining some of the coolant from the cooling system. You do not have to drain the entire radiator. Just open the drain valve and let out enough coolant so the coolant level in the engine is below the sensor.

This would be a good time to check the condition of the coolant, and to replace it if the coolant is more than three years old (conventional coolant) or five years old (long life coolant). A coolant change and a flush would also be a good idea if the coolant shows any signs of contamination.

The threads on the coolant sensor may be pre-coated with sealer to prevent coolant leaks. Tighten the sensor carefully to prevent damage.

Once the new sensor has been installed, you can refill the cooling system. Make sure all the air is out of the cooling system. Air trapped under the thermostat may cause the engine to overheat or the coolant sensor to not read correctly.

Idle speed control systems

Summary
Idle speed control systems maintain a suitable idle speed to prevent stalling, when additional loads are placed on the engine.

Base engine idle speed may be set by adjusting a screw on the throttle body. This sets how much air flows through a bypass passage, from the intake air side, to the manifold side of the throttle body.

However, if more load is put on the engine during idle, its idle speed may fall to a level where the engine stalls. Higher load can be caused by extra frictional resistance that occurs in a cold engine, and by electrical loads from headlights or the cooling fan. Shifting an automatic transmission into a drive range, or engaging the air-conditioner compressor clutch will also cause a drop in idle speed.

The extra air needed for a cold engine can come from an Auxiliary Air Device. This one has a connecting hose from the intake air side to its controlling passageway, and a return hose to the plenum chamber. It bypasses the throttle plate when it is operation, to provide the extra air. The control unit reacts to this additional air by metering additional fuel. This makes more air-fuel mixture available during the warm-up period.

How much air bypasses the throttle plate can be controlled automatically by the ECU. It receives data on idle speed and idle conditions, and uses it to provide an output to a solenoid-operated taper valve, or to a stepper-motor pintle. The valve varies the opening of the bypass passageway, and changes the idle speed to suit.

The position of the throttle plate can control idle speed automatically. A D-C motor works a plunger in contact with a lever, attached to the throttle spindle. As idle conditions change, the control unit can extend or retract the plunger, which increases or decreases the throttle plate opening. This provides the desired idle speed.

If the control unit is programmed to maintain a fine control of the idling speed - perhaps to within 100 RPM - ignition timing can be used. Advancing the ignition point increases engine speed, just as retarding it decreases it.

Engine Coolant Temperature SENSOR

P0115 - Engine Coolant Temperature Circuit Malfunction

OBD-II Trouble Code Technical Description

 Circuit Malfunction

What does that mean?

The ECT (Engine coolant temperature) sensor is basically a thermistor that changes resistance with temperature. Usually a two wire sensor, a 5Volt reference from PCM (Powertrain Control Module) and ground signal to PCM. This is different from a temperature SENDER (which usually operates the dash temperature gauge and operates in a similar way as the SENSOR, only it's a different circuit than what a P0115 is referring to). As the temperature of the coolant changes, the resistance changes on the ground signal to the PCM. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. If the PCM detects a voltage condition that seems abnormally low or high, P0115 will set.

Symptoms

Symptoms of a P0115 DTC code may include:

• MIL (Malfunction Indicator Lamp) illumination will always occur
• Vehicle may be hard to start
• May blow a lot of black smoke and run extremely rich
• Engine may want to die or backfire in tailpipe
• Engine may run lean and increased Nox emissions may be apparent (Requires gas analyzer)
• Cooling fans may run all the time when they shouldn't be, or not at all when they should be

Causes

Usually the cause can be traced to a bad ECT sensor, however that doesn't preclude the following:

• Wiring or connector damaged at sensor
• Open or short in reference or signal circuit
• Open or short in signal circuit
• Bad PCM

Possible Solutions

First, visually check the sensor for damage to wiring or connector and repair as necessary. Then, if you have access to a scanner, determine what the temperature of the engine is. (If you don't have access to a scan tool, using the dash temperature gauge may not be an effective way to determine coolant temperature. This is because the P0115 code is referring to the ECT SENSOR, and the dash gauge is operated by, usually a one-wire SENDER. Basically a different sensor that the code doesn't refer to.)

2. If the engine temperature is abnormally high, around 280 deg. F, that's abnormal. Unplug the sensor on the engine and see if the signal drops to, say, negative 50 deg. F. If it does, then it's a good bet the sensor is bad, internally shorted, causing a low resistance signal to be sent to the PCM. However if you want to be sure it's the sensor and not the wiring, there's a couple tests you can do. With the ECT sensor unplugged, check that you have 5 volts on the reference circuit with KOEO (Key on engine off). Also you can check the resistance of the sensor to ground using an Ohm meter. The resistance of a normal sensor to ground will vary a little depending on the vehicle, but basically, if the temp of the engine is around 200 deg. F., the resistance will be about 200 Ohms. If the temperature is about 0 def. F., the resistance will be over 10,000 Ohms. With this test you should be able to tell if the resistance of the sensor matches the temperature of the engine. If it's not accurate according to your engine's temperature, then you probably have a bad sensor.

3. Now, if the temperature of the engine according to the scanner is around 280 deg. F. and unplugging the sensor doesn't cause the reading to drop to negative 50 deg. F, but it stays at the same high temperature reading, then you'll need to repair the short on the signal circuit(ground) to the PCM. It's shorted directly to ground somewhere.

4. If your temperature reading of the engine according to the scanner is showing negative 50 deg. F or so, (and you don't live in the arctic!) unplug the sensor and check for a 5V reference present at the sensor.

5. If there isn't, then check at the PCM connector for proper 5V reference. If it's present at the PCM connector, then repair the open or short on 5V reference from PCM. If there is no 5V reference present at the PCM connector, then you're done with your diagnosis and you may have a PCM fault. 6. If the 5V reference circuit is intact, then check the ground signal to the PCM using the previous ground resistance test. If the resistance isn't normal for the temperature of the engine, then ohm the resistance of the ground signal to the PCM by removing the ground signal wire from the PCM connector. The wire should have no resistance, unplugged from the PCM to the sensor. If it does, repair open in the signal to the PCM. If it doesn't have any resistance on the ground signal wire and the resistance test of the sensor is normal, then suspect a faulty PCM.

Other coolant engine light codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128

How often should I change my antifreeze?

For “ordinary” antifreeze, the vehicle manufacturers generally recommend coolant changes every two to three years or 30,000 miles. Others say it’s not a bad idea to change the coolant every year for maximum corrosion protection — especially in vehicles that have aluminum heads, blocks or radiators. But such recommendations may soon be obsolete. Several antifreeze suppliers have just recently introduced “long life” antifreeze formulations that claim to provide protection for four years or 50,000 miles.General Motors just introduced a new five year, 100,000 mile antifreeze in its 1996 cars and light trucks. The new coolant is called “Dex-Cool” and is dyed orange to distinguish it from ordinary antifreeze (which is green).CAUTION: These new long life coolants provide extended life only when used in a clean system mixed with water. If mixed with ordinary antifreeze and/or old coolant in a system, the corrosion protection is reduced to that of normal antifreeze (2 to 3 years and 30,000 miles).CORROSION INHIBITORSThe life of the antifreeze depends on it’s ability to inhibit corrosion. Silicates, phosphates and/or borates are used as corrosion inhibitors to keep the solution alkaline. As long as the antifreeze remains so, corrosion is held in check and there’s no need to change the coolant. But as the corrosion inhibiting chemicals are used up over time, electrolytic corrosion starts to eat away at the metal inside the engine and radiator. Aluminum is especially vulnerable to corrosion and can turn to Swiss cheese rather quickly when conditions are right. Solder bloom can also form in copper\brass radiators causing leaks and restrictions. So changing the coolant periodically as preventative maintenance is a good way to prevent costly repairs.The basic idea is to change the coolant before the corrosion inhibitors reach dangerously low levels. Following the OEM change recommendations is usually good enough to keep corrosion in check, but it may not always be the case. That’s why more frequent changes may be recommended to minimize the risk of corrosion in bimetal engines and aluminum radiators.CHECKING THE ANTIFREEZEOne way to find out if it’s time to change the antifreeze is to test it. Several suppliers make special antifreeze test strips that react to the pH (alkalinity) of the coolant and change color. If the test strip indicates a marginal or bad condition, the coolant should be changed.CHANGING THE COOLANTReverse flushing is the best way to change the coolant because draining alone can leave as much as 30 to 50% of the old coolant in the engine block. Reverse flushing also helps dislodge deposits and scale which can interfere with good heat transfer.The concentration of antifreeze in the coolant also needs to be checked prior to the onset of cold weather. A 50/50 mixture of antifreeze and water is recommended and will protect against freezing down to -34 degrees F and boilover protection to 263 degrees F.For maximum protection, up to a 70% mixture of antifreeze can be used for freezing protection to -84 degrees F.CAUTION: Do not use more than 70% antifreeze, and never run straight water in the cooling system because it offers no corrosion, freezing or boilover protection.

Flushing the System RADIATOR

The original additives in antifreeze fight rust and corrosion breakdown and are ineffective after 1 to 2 years. This is because of the continual exposure to the heat in the cooling system. After the additives break down, rust begins to form rapidly. Therefore, a rust-colored antifreeze is an indication that the cooling-system service is required.

The cooling system should be cleaned periodically to remove rust, scale, grease, oil, and any acids formed by exhaust-gas leakage into the coolant. Recommendations vary; for example, Chevrolet recommends that the cooling system be drained and flushed every 2 years.

Flushing (cleaning) of a cooling system should be done based on the manufacturer’s recommendations or when rust and other contaminants are found in the system. Flushing involves running water or a cleaning chemical through the cooling system to wash out contaminants. Rust is very harmful to the cooling system because it causes premature water pump wear and can collect and clog the radiator or heater core tubes. There are three methods of flushing-fast flushing, reverse flushing, and chemical flushing.

Fast flushing is a common method of cleaning a cooling system because the thermostat does not have to be removed from the engine. A water hose is connected to a heated hose fitting. The radiator cap is removed and the petcock is opened. When the water hose is ON and water flows through the system, loose rust and scale are removed.

Reverse flushing of a radiator requires a special flushing gun device that is connected to the radiator outlet tank by a piece of hose (fig. 6-14 ). Another hose is attached to the inlet tank, so the water and debris can be directed to the floor drains. Compressed air, under low pressure, is used to force water through the radiator core backwards. The air pressure is used intermittently to loosen scale and sediment. Excessive air pressure should be avoided to prevent damage to the radiator. Starting and stopping the water flow produces a fluctuation in pressure and tends to loosen all foreign matter clinging to the passages in the radiator core.

Reverse flushing can also be used on the engine block and head (fig. 6-15 ). First, remove the thermostat and disconnect the upper radiator hose. Then disconnect the lower radiator hose at the water pump. Insert the flushing equipment in the upper radiator hose.

Reverse flush the system by sending water and air through the water jackets and coolant passages. Following the flushing, replace the thermostat and hoses so the system can be refilled.

When reverse flushing equipment is not available, you can still reverse flush the system with a garden hose. This is often effective following the use of a chemical cleaner.

Chemical flushing is needed when a scale buildup in the system is causing engine overheating. Add the chemical cleaner to the coolant. Run the engine at fast idle for about 20 minutes. Wait for the engine to cool. Then drain out the coolant and cleaner solution. Using a garden hose, flush out the loosened rust and scale. Continue to flush until the water runs clear.

CAUTION

Always follow manufacturer’s instructions when using a cooling system cleaning agent. Wear protective gloves and goggles when handling cleaning agents. Chemicals may cause eye and skin burns.

How to Mix Car Coolant

On its own, coolant helps your car flush built-up heat out of its radiator to prevent your car from overheating. However, if you mix coolant with water in the proper ratio, you can also reap the benefits of the coolant's or antifreeze's anti-corrosive properties. You'll need to consult your car's owner's manual to learn the proper specifications for use of antifreeze or coolant, but there are several general principles to keep in mind when you mix car coolant with water.

Other People Are Reading

• How to Mix & Add Engine Coolant
• How to Mix Engine Coolant

Instruction

1. • 1
     Consult your car's manual. There will be a section dedicated to coolant or antifreeze-usage specifications. If you cannot find this information, contact your car's manufacturer to learn the specs you need to know before proceeding.
   • 2
     Stick to brand-name coolants, such as Prestone and ThermalTake.
   • 
     

     • 
       
   • 3
     Mix your antifreeze at a one-to-one ratio with water. For temperate climates, this will provide the protection you need in winter weather and effectively work to keep your engine from overheating. In addition, a 50/50 coolant-to-water ratio fights rust, boiling and engine corrosion.
   • 4
     Mix an ethylene-glycol coolant with water in a 70:30 ratio (in other words, 70-percent coolant to 30-percent water). This is recommended if you live in an environment that experiences harsh winter weather. It is also the highest coolant-to-water ratio that most experts recommend for use in car engines.
   • 5
     Combine factory antifreeze or coolant products, such as DEX-COOL, with water at a ratio not exceeding 60:40 (60-percent antifreeze or coolant to 40-percent water). Mixing a long-life factory antifreeze product like DEX-COOL with water does not take away from its efficacy and may actually help it last longer. However, combining DEX-COOL with other coolant or antifreeze products can diminish its potency.
   • 6
     Make absolutely certain that both your car's engine and coolant system are completely cool before you begin to work with them. When you have drained your car's coolant system and achieved the proper mixture of antifreeze or coolant and water, refill your car's coolant system with the appropriate solution and hit the road.
   • 7
     Learn more about coolant on the Road & Travel Magazine website (see Resources below).

Tips & Warnings

• While a long-life factory antifreeze product will have a life of 5 years or 150,000 miles, you will shorten this lifespan if you mix it with other coolant products. Many people simply mix ethylene-glycol coolant with their existing antifreeze because they don't realize they're actually compromising the overall efficacy of their coolant.
• It is best not to mix different types of coolant or antifreeze with one another, unless it is unavoidable. A much better solution is to drain your car's coolant system and refill it with a single coolant-and-water mixture.
• Use softened water whenever possible. Hard water can affect the chemical makeup of some coolant products.

| eHow.com