QuestionQUESTION: Hello, my daughter has a 2005 Pacifica, 3.8l. She's had many problems with this car. The latest problem seems to be the ECU. Here's what happened. The car started running really rough, shifting hard, stalling. A friend of hers who claims to be a mechanic hooked up his code reader and three different codes showed up. EGR valve, throttle position sensor, and one other sensor that I don't remember. He replaced the EGR and supposedly the other codes went away. A couple days later my daughter drove about a mile to the gas station and the car wouldn't start for her. She had someone give her a jump and the car started. She drove a few blocks and she said the lights got dim and the car died. She called me and I went and jumped the car and it started. She went a few more blocks and it killed again so I had to jump it one more time. This was the last time that the car has been running. I assumed that she had either a dead battery, a bad battery, or a bad connection somewhere. I charged the battery fully and the car wouldn't turn over. It won't even turn over with a jump now. Just a slight click coming from the fuse box next to the battery when we turn the key. Her mechanic friend came over and hooked up his code reader but he couldn't get it to recognize the ECU. We checked all of the connections that we could find including grounds. She had the car towed to a repair shop and the tech spent some time on it and has determined that the ECU is bad. He wants $1200 to repair it, $800 for the ECU and $400 for labor. My daughter can't afford that. I was able to find a few used ECU's around the area but I'm not sure if they can be trusted to be good. My questions are, if I get a used ECU that came from the same model year Pacifica with the same engine, can I just replace the old one with it and assume that it should work? Is $400 a reasonable amount for labor on a job like this? Why would the ECU fail in the first place? Do you have any suggestions for me?
ANSWER: Hi Dan,
From what you described as the history of the problem I would not believe that a failed ECU/PCM is the cause of it. I assume that the issue first of all is the starter motor now will not turn over the crankshaft. That task is almost devoid of involvement by the PCM but in any case my approach would be to see if you can get the starter motor to crank over the engine when you by-pass the PCM. By the way the fact that you heard a soft click from the integrated power module box near the battery when you turned the key to start is indicative that the PCM is NOT preventing the starter from firing as its main point of intervention is exactly at the location of the click, e.g. the starter motor relay which is closing as it should. If that clicks, then the PCM is not stopping the starter motor from responding.
I would suggest that you do a jump from the battery to the yellow/gray wire on the starter's solenoid switch as that will test the battery as well as the starter motor. It may well be that there is a short circuit that is draining the battery or the starter motor itself may be faulty. There should be a loud click from the starter motor solenoid switch if there is 12.5V or more on it coming from a jump from the + post of a charged up battery. If that happens and the starter motor doesn't respond then either the starter motor is the problem, or the fat red wire from the battery to the starter is bad, or one of the battery - post grounding wires is loose or corroded at its far end. So you would check all those possibilities. Also measure what is the current flow through the battery when everything is shut off (lights, etc.). That 'ignition off draw' should be less that 0.2 amp measured by an ammeter inserted between the - post of the battery and the removed - post battery clamp.
I would not change out the ECU/PCM until you have starter motor action in the normal fashion, and even then I would look further before replacing the PCM. Do another fault code readout before doing that and let me know what you find. Let me know if the starter is now working but the engine won't catch and run.
While I wrote this in the context that you would do these things, of course show this to the mechanic at the shop if the vehicle is still there.
Please read the PS (below) and respond to it.
Roland
---------- FOLLOW-UP ----------
QUESTION: So, I spoke to the mechanic and he said that he jumped the starter and turns over the engine just fine. He says that the power is getting to the starter relay from the key but the ECU/PCM is not grounding the starter relay as it should to send power through to the starter. He also said that his scan tool will not communicate with the ECU/PCM. He said it can see other components in the system but not the ECU/PCM. One other thing, the plastic shroud that goes inside of the left front fender around the wheel, is missing. The mechanic said that the ECU/PCM is located right in front of the front left left wheel and it's all full of road grime up in there. He said that this could be the root cause of the ECU/PCM failure. Your thoughts? Also, if I get a used ECU/PCM that came from the same model year Pacifica with the same engine, can I just replace the old one with it and assume that it should work?
AnswerHi Dan,
The one problem I have with that explanation is that you said that you heard a soft click when you tried the starter, back in the history of this situation. That would show that the PCM was grounding the starter relay at that point in time, otherwise it wouldn't have clicked. Maybe the battery is too weak to even cause the relay to click at this point in time due to a short circuit. The history of this does suggest there is a short circuit that drains the battery.
Before opting to replace the PCM I would go to the shop and verify now that there is no longer a soft click sound when you try to start with the key (and that the battery is indeed charged), and if not also try to start with the key AFTER having grounded the dark green/orange wire (accessible either at pin 3 of the gray 10-pin plug of the power module or pin 38 of the black/natural (in side) plug of the PCM) to verify that the relay circuit is working when the that wire is grounded but not working when you simply try the key to start it. The PCM is supposed to ground that wire if it is working and the trans is in park or neutral). If it appears to not be doing that then I would suggest that the PCM be removed and the plugs and sockets be de-grimed and then try it again. The grime may be what is affecting the functioning of/communication with the PCM.
A used PCM with the same part number and from the same year/engine of Pacifica should work, but the VIN and odometer reading should be entered into it, and more important if the ignition key has a bulge in its handle (and thus a security key immobilizer system then the 'secret key' number has to also be entered into the replacement PCM or it won't allow a start). And the trans control module also has to be "verified" even though not replaced. I have the pages that describe these 'verifications' when a control module is replaced and hopefully the mechanic's diagnostic box can do them. Maybe a dealer would be a better place to have the pcm replaced for that reason.
For all these reasons I would want to be very sure that the existing PCM can't be made to work by de-griming it if indeed it is the cause of the no-starter. It seems one gets into further problems unnecessarily by replacing the PCM if you can get it to work.
Thanks for the rating and nomination, which you can do both of those again if you believe I merit that.
Roland
