QuestionQUESTION: hi, i live in Australia and have had multiple problems lately with my 1997 3.3L voyager se.
firstly it is a dual fuel vehicle and have had idle issues with both systems but mainly the petrol. the car tends to stall or rev/idle either too low or too high, i had the fuel pump and the gas converter replaced about 4 or 5 months ago due to a ?fuel insufficiency? the car ran fine for a period then developed similar symptoms and is now almost impossible to run on petrol. the mechanic has had it back at the garage several times free of charge trying to find a solution, and tells me the computer needs to be replaced, something to do with the volt reading telling the computer the throttle is open? sorry if that's not clear. I'm also told that I'll need an immobilizer from the same car the computer came from in order for the two parts to communicate properly.
the current issue is the thermo/engine cooling fan has turned itself on about an hour after the engine was turned off. it stayed on after starting the engine for a few minutes and in the end i needed to disconnect the battery. several hours later i reconnected the battery only to find the thermo fan turned on after the battery was connected for about an hour. I've just taken the fuse out(it appears unbroken) the fan stops running without a fuse but i don't want to drive the car without a fan at all. could this be related to my computer problems or a separate issue.
ANSWER: Hi Mark,
My first thought is that the fan relay is stuck 'on', rather than that there is a failure of the pcm. It is located under intake air box on the left side frame rail very near the rear side of the radiator. You can trace the wires from the fan module to find it. That solid-state relay was failure-prone and in fact was subject to a recall for free replacement by Chrysler. You could disconnect the plug for the relay and then measure for either continuity or 'open' between pins 3 and 4 of the socket (the ones for the dark green and the gray wires). With the unit unplugged it should be open. The pcm closes the relay by grounding pin 2 (light green/dark blue wire) when it senses the temperature of the engine coolant has reached the level needed to activate the fans. If the relay tests ok, then the next time you have the problem with the fans coming on when the engine is off, pull the plug and re-measure between 3 and 4. Also check to see if the light green/dark blue wire shows it to be shorted to ground (0 ohms resistance compared to ground). That way you will be able to sort out whether it is the relay coming on by itself or the pcm that is falsely turning on the relay.
Because this is a '97 (verify that the 10th position of the VIN is a U) you should be able to get some indication of what the pcm thinks might be wrong with the engine, by means of the ignition key. Turn the key 'on-off-on-off-on and leave on' doing that in 5 seconds or less elapsed time. Then watch the 'check engine' light, which remains 'on', to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat the process to be sure of an accurate set of flash counts. Then tell me the counts in order of appearance and we'll go from there.
There would be a code for a faulty computer if that is the case.
The throttle position sensor is powered by 5V, which arrives on a violet/white wire at its plug. I believe you would find that the voltage on the signal wire (orange/dark blue) would be low when the throttle is closed and rise by about 3V from the low reading when you have the throttle fully open, making the reading between the orange/dark blue and the light blue/black wires.
We may get other codes that would point toward a cause for the poor idle.
I would avoid changing the pcm because as you note there needs to be communication between it and body control module which handles the immobilizer function, and that requires programming them to recognize one another, and also the pcm does have to be designed to recognize the immobilizer commands from the bcm.
Roland
---------- FOLLOW-UP ----------
QUESTION: thank you for your assistance thus far.
the plate under the hood states it is a 02/97 model but the 10th position of the vin shows a V. 11th is U. also there is a plug just below the fuses near the steering wheel that states "for diagnostic use". i attempted the on off on off on process anyway but i have no flashing lights on the dash to read for a code.
i will try to measure the indicated plugs in the next 24hours and let you know how i go.
thank you again
AnswerHi Mark,
That U means it is a '97 model. If the check engine light doesn't flash after the 'on-off.." (which is an OBD-I code technique which was phased out in '96/7) then the code readout is via plug you found using an OBD-II code reader. Let me know what 4-digit numbers come out.
