91 Caravan - Computer Problems?

91 Grand Caravan SE (ABS,DIS,AWD,3.3L)

I think I have a computer problem or, it could be that multiple problems started all at once.

First Problem: Air conditioner quit, radiator fan stopped.

I found a fusible link burnt. I replaced it and realized A/C fan was seized and blew fuse again. Disconnected A/C fan, replaced fusible link. A/C works but no fan of course. Still no radiator fan. I replaced 'Cooling Fan Relay' - no help. Radiator fan works, I connected to a switch for now.

Question: Could the 'Coolant Temperature Sensor' be bad if the analog temp gauge works?

Second Problem: Intermittent miss at decel and low RPM

The day of overheating, I could not idle. The engine ran fine under load and at +2000RPM. Let off the pedal and it sputted and died. Changed fuel filter, air filter, oil - No Help. This continued to happen intermittently (hot and cold) for about three days until problem #3 cropped up.


Third Problem: Dies suddenly (random temp & time), won't Start for random time period.

No spark. No 'Check Engine' light. I checked fault codes and it says I have a bad O2 sensor (51), MAP (13), AIS (25), Fan Relay (35) and Code 11, even if car started last time I checked. Pulled battery overnight to clear codes, same codes without starting vehicle. Same codes after starting vehicle. Same codes after vehicle dies. I changed the ASD relay.

'Check Engine' light goes out after 3 seconds. I don't want to spend hundreds on sensors to find out the computer is bad. HELP!!!!!!

Questions:

Do you think I have a bad computer?

What is the curved module against the fenderwell on the driver side where the test connector is?

What is the square module against the firewall on the passenger side?

Your questions:
1. No, your computer is likely OK
2. That is your computer (ECM)
3. Don't know

Your cooling fan circuit:

4. The temperature switch is seperate from the temperature sensor for the gages.

Power from the ignition goes to the temperature switch located at the bottom of the radiator. When the temperature there get hot, the switch sends power to the cooling fan relay. The relay sends power to the cooling fan motor over a seperate circuit.

The correct procedure to reset the computer codes (80-95 cars) is to turn the ignition switch on-off-on 50-55 times. No need to start the engine. Computer codes are only stored for 50 starts and get aged out.

Stall problem:
One code being set can cause multiple codes to be set. You also may have some older codes lingering about.

Of the codes listed, ignore the 51 (oxy. sens), the 25 (idle can't be maintained), and 35 (fan relay).

The most probably one(s) is/are the 13 (map sensor) and possibly the 11 (lost timing signal).

The map sensor measures vacuum and is used to deturmine (with the throttle position sensor and the air temperature sensor) how much gas to give the engine.

The loss of the timing signal code relates to the signal from the distributor for cylinder firing. The timing comes from the crankshaft speed sensor (timing mark for number one cyl.) and the camshaft sensor (magnets located within the distributor).

Possible causes:

Note found on oxygen sensor description:

51 Oxygen sensor stuck at lean position may be tripped by a bad MAP sensor system causing a rich condition, and the O2 sensor trying to compensate. The O2 sensor may still be good. The MAP assembly consists of two pieces, the valve and the vacuum transducer (round plastic unit with cylinder on top and both electrical and vacuum connections) - If you get hot rough idle and stalling, especially on deceleration, accompanied by flooded engine and difficulty restarting, that can be a bad MAP sensor causing the O2 sensor to try to compensate. If you get poor cold driveability, stumbling and bucking, and acceptable warm driving with poor gas mileage (a drop of 10 mpg or more), that is usually the O2 sensor. [Webmaster note: MAP sensors seem to die regularly.]

The other possiblility (timing related) could be the crankshaft speed sensor. Does the speedometer bounce? Is the sensor oily?

Hope that gives you a start.

It was not the computer; at least not for the 'Dies Suddenly / No Start / Starts OK Later' issue. I think I may also have the Miss on Decel and Idle fixed but only time will tell.

It was an intermittent wire connection at the connector for the Ignition Reference Sensor (Crankshaft Position Sensor). Someone had replaced the Knock Sensor and used a new style of wiring assembly. When they did, the old wire was secured to the harness with a wire tie. The wire tie had put stress on the Crankcase sensor wiring and I assume the wire was damaged due to engine vibration and heat.

I have not solved the Radiator Fan issue. There is no sensor on the radiator that I can find. I went to the junkyard and cut open a harness; I traced every wire going to the fan and relay. It is impossible from the Chilton's manual to tell if the gauge and computer use the same sensor (my gauge is accurate). The relay has been double checked. There is power to the relay; when I short across the relay connector, the fan works.

The crankshaft position sensor is located in about the worst possible place for a transverse engine. I assume tune up guy have no problem but my fat fingers had a real problem. The best access is from under the vehicle (the same place as spark plug access).

The module on the firewall is still a big question. I assume it is either part of the Airbag, ABS or AWD system. None of the vehicles in the junkyard had this module or harness but none of them were AWD or ABS.

The SBEC now shows no faults. I am still concerned that I had so many sensor faults and no 'Check Engine' light.

I pulled the wire going to my Coolant Temperature Sensor and the temperature gauge still worked. After I pulled the wire I got a Coolant Sensor Fault proving the connector and cable are OK. The Chiltons wiring diagram does not show an additional sensor for the gauge; go figure.

I changed the sensor and still no radiator fan. This is the sensor located under the coil pack. I can find no other sensor on the radiator or engine block.

Summary of Problem:

91 Caravan 3.3L DIS, AWD, ABS

Air Conditioner Fan siezed and burnt fusible link; coolant fan also stopped. Replaced link and air conditioning fan which works fine but still no coolant fan. Have wired fan with switch for now.

1. Tried new relay
2. Tested wiring (shorted across relay; works fine)
3. Reseated SBEC Connector
4. Reseated unknown module on firewall connector.
5. Replaced coolant temperature sensor.
6. Checked coil voltage at relay connector.

Here's the stumper. I have 12V on one side of the connector where the relay coil connects and 0V on the other. What I know about relay's, this should be closing the contacts. The only thing I can figure is that when the relay is installed both sides go to 12V because the SBEC is not sinking any current. I still think I have a computer problem!!! I am going to sandwich some wires in with the contacts of the relay so I can measure the coil voltage with the relay in circuit but it's dark now.

Any help appreciated.

I still have this problem.

I am sure everything from the relay to the fan isworking fine, I can control the relay and make it work.

There is no sensor on the radiator itself.

I changed the sensor near the thermostat.

It does not come on when I engage the A/C. The manual says the fan will always be on when A/C is on. The A/C fan does work, they are on the same fusible link.

When you unplugged the coolant temperature sensor for the computer, did the fan come on then? On all of the Chrysler vehicles that I have seen, when you unplug the sensor, the fan is supposed to come on, part for a dignostic reason, and the other reason is that if that sensor died, it is better to have the fan on all the time than not at all.

I know on my 3.0 you unplug that sensor when you have to set the base engine timing.

If you unplug that sensor and the fan does not come on, and the wire from the computer to the cooling fan relay is good, then I would say your computer is bad, or at least that output is bad.