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2003 Caravan: Do I need a new PCM?

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  #1  
Old 05-31-2009, 05:26 PM
mrm mrm is offline
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Default 2003 Caravan: Do I need a new PCM?

I have a no-crank situation in my 2003 Grand Caravan with 3.3 engine.

The starter relay has no ground on pin 85, which is the ground side of the coil. As I understand it, that ground comes from the PCM.

My cheap OBD II scanner doesn't get any codes.

I've tried the on-off-on-off-on thing, and nothing happens. I'm not sure what I'm looking for, or that I'm doing it right, but nothing on the dash blinks when I'm finished.

When I short across the start relay, the engine cranks, but I have no spark, and I never hear the fuel pump running.

All of the fuses and fusible links near the battery are good. If there are other fuses, I don't know about them.


I'm pretty sure that all of this adds up to a bad PCM, but is there anything else it could be? Are there other troubleshooting steps I should try? I want to be confident in my diagnosis before I spring for a new computer.

Thanks!
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  #2  
Old 05-31-2009, 09:22 PM
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can't help with what all the problems add up too.. but did want to add this...

I had a 96 Caravan Sport (now have an 06 Grand Caravan)... but in 2003 I had a no start situation... would just crank and crank... friend helped me replace the cam position sensor..still the same... broke down and had it towed to my Dodge dealer and they actually REPLACED the PCM (whole computer) under the 7/70 warranty for free!.... I only had about 65k miles on it, but it must have come in just under the wire to cover a 96 in 2003.
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Old 06-01-2009, 10:07 AM
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I've pulled the computer out to have a look. There are 3 TO-220 packaged components on the board.
Click the image to open in full size.

It's tough to make out in my pictures, but one of them looks discolored, and the potting goo around it is discolored as well. It's the one directly between two large capacitors:
Click the image to open in full size.

Here's the whole album, including hi-res shots.

I still don't know for sure that the PCM is bad, but this component sure doesn't look happy.
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Old 06-03-2009, 12:03 AM
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Did you omh test the ground wire from pin 85 to the PCM? You could have an open wire.
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Old 06-03-2009, 03:37 PM
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Quote:
Originally Posted by master tech View Post
Did you omh test the ground wire from pin 85 to the PCM? You could have an open wire.
I have not tried that because I don't have a wiring diagram which would tell me which pin (or even which connector) to probe.

...But I don't think it's a problem with that wire because I don't have fuel or spark either.

Can you tell me where to find the other end of pin 85 on the computer harness?

Thanks!
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Old 06-03-2009, 10:29 PM
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The PCM may not be the problem, Hook the PCM back into the van. Using a 12v test lite, hook the clamp end to pos battery and ck the pin 85 with the other end. if your test lites up, then you have ground. You may have a bad front control module.
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Old 06-04-2009, 09:09 AM
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There's definitely no ground at the starter relay's pin 85.

I've probed through the PCM connectors and found continuity to the start relay coil (pin 85) on pin 31 of one of the PCM connectors.

I think I can conclusively say that the PCM is supposed to ground the start relay, and that the wiring is good.

It's still not clear why the PCM isn't grounding the relay.

It could be that the PCM needs to be replaced, or it could be that the PCM has detected some other error condition, and is refusing to cooperate as a result.

What's the front control module?

Thanks for your help!
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Old 06-04-2009, 10:10 PM
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Supplys power and ground to relays and fuses. Its bolted to the PDC box.
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Old 06-16-2009, 05:58 PM
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Default Fixed!

Well, the problem is resolved.

I didn't do any more diagnosis, except to confirm PCM continutiy to pin 85, and switched voltage at the PCM when the key is in the "start" position. I found these pins (and learned about the "start" pin) from the haynes manual, but had to find the specific pins by wire color. No fun with 80 wires in the harness.

Oh, I ordered both Haynes and Chilton manuals. They're the same books. First time I've seen that. Big disappointment.


I ordered a rebuilt PCM from "all computer rebuilders". I'd considered ordering from "solo", but went with the other guys.

...and imagine my surprise: The UPS labels said "solo". Maybe the same company? Maybe they have a reciprocal arrangement when one is out of stock? I seem to remember the ACR guy saying something about stock levels and an "alternate source".

I gave ACR my VIN, mileage and $295. I received:
  • The PCM compatible with flex-fuel vehicles (E85 sticker in the fuel door)
  • A mounting plate installed onto the PCM
  • A "warranty void if removed" sticker preventing me from looking at the PCM innards I've photographed for this thread
  • A shipping label for the return of my old PCM
The van fired right up, and has been working great. No check engine light, and no problems so far.

I have not tried pulling codes, and I'm due for the state inspection before the end of this month.

Fingers crossed.
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03, 2003, 85, bad, caravan, compatibility, dodge, grand, ground, pcm, pin, solo, update, vin, whats

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