QuestionQUESTION: Hi,
Have this car trouble free since new. No accidents. No major repairs.
When the ignition is in the on position the asd relay, fuel pump relay and egr solenoid constantly chatter and the check engine light constantly flashes on and off. If I put a test light on the B+ lead to the ignition coil it also constantly flashes on and off. There are no codes.
When the ignition is in the start position the best I can describe is a pulsating type of crank.
When the ignition is in the off position the fuel pump relay and egr solenoid stop chattering and the check engine light no longer flashes on and off but the asd relay continues and if I put a test light on the B+ lead to the ignition coil it also continues to flash on and off. If I remove the relay while this is happening I get a constant 12+ volts at cavity 30 and 86. If I connect a test light from the positive terminal of the battery to cavity 85 the light constantly flashes on and off. I checked the circuit from cavity 85 to the pcm for continuity and shorts. Thanks.
Steve
ANSWER: Hi Steve,
That last observation about the test light flashing on and off at cavity 85 is important, but was that with or without the asd relay in the socket, and I presume the ignition off?
If it was with the relay removed, then it sounds to me like there is a marginal voltage supply to the pcm that is causing it to spontaneously oscillate that between 12v and ground on pin 85 rather than holding 12v until you turn the ignition to the run position. What is voltage showing across the battery during this condition? And is it the same at pin 46 of the pcm?
What is the current being drawn from the battery when all the doors are closed, etc. so that there are no lights on, which is the 'ignition off draw' in mA. It should be about 25-50 mA.
I would wonder if either the battery voltage is low or there is a short that is drawing the voltage down which the IOD mA reading would tell us.
All the activation coils of the relays and the solenoids depend upon there being something close to 12v for them to close positively, so that is why I ask. How old is the battery compared to its warranty life?
You have done a good job of sleuthing so far, we just have to find out why the ASD driver, pin 85/pcm 67 is flaking out that way. Would have a way of jumping a better battery into the sitution?
Roland
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QUESTION: Roland,
The following are answers to your questions and the results of tests you suggested:
Yes, the test light was flashing at cavity 85 without the asd relay in the socket and with the ignition in the off position.
The battery is in the first month of an 84 month warranty.
The voltage across the battery with the asd relay removed and the ignition in the off position is 12.24 volts. The voltage at pin 46 of the pcm is 12.38 volts. In order to check the voltage at this pin I removed the pcm connectors which stopped the chattering asd relay.
With everything off, the DC current across the IOD fuse socket with the fuse removed is a constant 38mA. I am not sure if this was the correct way to check this?
You should know that the chattering asd relay with ignition off condition occurs only after the ignition is first switched to the on position.
I am determined to resolve this problem so if there is anything else you would like me to check don't hesitate to ask. Thanks.
Steve
ANSWER: Hi Steve,
I have never experienced/heard of that sort of behavior on the asd 'driver' wire (pin 85). That driver is controlled by the PCM and it is supposed to turn the ASD 'on' for 1 second when you turn the key to 'run'. Then in the absence of any pulsing from the engine rotation sensors it should not activate the ASD again (by grounding pin 85) until you use the starter motor which energizes the pulsing of the rotational sensors which the PCM 'sees' and at that point turns the ASD on again for as long as you crank it or until the engine starts.
I suspect the PCM is bad because I can't think of anything that would give the impression that the engine is running or that the ignition is pulsating on and off (unless there is a flakey ignition switch which I can't see doing pulsations). If you can get a used pcm from a '98 van with the 3.3L and the same set up as far as vehicle theft security and remote key fob accessories that would be my suggestion. You would need to have it programmed with the VIN number to mate it to the bcm and tcm properly.
One test you might try is to remove the plugs on the pcm and then apply 12v to pin 46 and ground pins 10 and 50, then put your voltmeter on pin 67 (asd relay control wire) and finally apply 12v to pin 20 which is the ignition switch output wire. Then see if you get pulsing under these minimal input conditions. If so, I would believe that corroborates a bad pcm.
When you originally said "no codes" does that mean it gives no sign of reading codes, or that it does and says 'done'? If it isn't showing codes and doesn't show evidence of having tried (done) to read them out that would also implicate the pcm. I haven't heard of this before, but then seldom to pcm's fail. I'll be interested to know how this resolves.
Roland
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QUESTION: Hi Roland,
My code reader read "no codes" after indicating that it was scanning. For what it is worth it does the same thing with both pcm connectors unplugged. My code reader is an off brand. Others may work differently.
I tried the test you suggested except that I used a test light on pin 67. When I first simulated ignition-on by applying 12 volts to pin 20 the test light flashed once for a second an went out. A few seconds later it began to continuously flash(slow at first but then a rapid pulsating); and when I removed the voltage from pin 20 it continued to flash.
I want to celebrate except that I have one nagging question. Since this test separates the pcm from the rest of the vehicle, would the absence of input from the rotation sensors or anything else create the same condition?
I may have access to a pcm(same part # from another vehicle exactly like mine). Can I temporarily install the pcm without changing the vin or mating it to the bcm and tcm whatever that means? Thanks.
Steve
AnswerHi Steve,
I would think that your test shows that the pcm is bad, but I can't guarantee that. I can't see how the asd relay's control is dependent upon there being the other sensors present.
There would be no problem with temporarily installing the pcm so at least you could see if the clicking of the asd relay stops.
You would want to be very careful to not 'arm' the anti-theft system until you have the programming done so that all the modules involved in preventing theft recognize one another. So after you install it, make sure that no uses the power door lock, door keys, or the remote fob to secure the vehicle. Only lock it up by using the mechanical push buttons.
Roland
