[FIXED] 2000 Chrysler Town & Country 3.3 No crank/No start

Initial symptoms: No crank/no start, no flash of CHECK ENGINE light when key turned to START.

Working at the Starter relay, there is 12V at all times to the load supply relay contact 30. Relay contact load ground side contact 87 shows a good path to ground through starter motor. There is 12v to the supply side control contact 86 with key on START, but kind of a "fuzzy" ground at contact 85, which is grounded at the PCM.

When I supply ground to relay contact 85, the engine will crank but I still get no spark (verified by checking voltage of input wires to coil packs)

So, at this point, given the fuzzy ground, and the non-illumination of the CEL, and the bad PCM-supplied ground, and the fact that supplying a good ground restores the crank, I am suspecting a bad PCM.

I have also checked the 5v reference circuit at the TPS and MAP sensors with KOEO, and it reads 0 volts at the sensors. I also back probed the 5v reference wire at the computer, and it reads 0 volts there as well.

I have checked the PCM ground wires that come out of the back of the PCM to the body ground, and they show as good grounds.

So, to my untrained eye, it seems we are looking at a bad PCM. What do you guys think? What else should I check?

Definitely on the right track with a PCM issue. You caught the big red flag with the lack of CEL operation

I saw that you've gone over the PCM grounds, but I'd suggest going over the power circuits, too. I know, it doesn't make sense that a lack of ground is caused by a power supply issue, but I still feel that it's worth checking. It may be that only part of the PCM is getting powered up, causing outputs to act weirdly. Could definitely explain the 5V reference issue, too.

The fuzzy ground from the PCM kinda makes me suspect a voltage drop issue, but that wouldn't explain the 5V reference... Perhaps worth rechecking that circuit at the PCM? Include pin fitment in there, too.

you could cut the 5 volt ref wire close to the pcm and then check for 5 volts. maybe a bad sensor pulling it to ground. thatd save you time from possibly unplugging all the sensors and still have 0 volts

cheryl hartkorn wrote: you could cut the 5 volt ref wire close to the pcm and then check for 5 volts. maybe a bad sensor pulling it to ground. thatd save you time from possibly unplugging all the sensors and still have 0 volts

That would be my next move!

That will be my next move as well!

I agree with isolating the 5v ref from the sensors before condemning the pcm. I have seen shorted sensors cause similar issues.

Unless there are 7 different 5v ref wires like that Cobalt I did with the bad ECM. (Two part series and I think it was a Cobalt)

Well after two fuel pump replacements on other vehicles (my Suburban, and my son's Mystique, both correctly diagnosed and repaired, I am glad to report) I am FINALLY back to this project. I cut the 5V reference wire near the PCM, and it shows .1 volt with negative polarity on my Power Probe. I am going to double check a few other things, but this is looking like a bad PCM to me...

popoften wrote: I cut the 5V reference wire near the PCM, and it shows .1 volt with negative polarity on my Power Probe. I am going to double check a few other things, but this is looking like a bad PCM to me...

The green 'negative' LED lit up? Hmmmmm, sounds like it's finding a path to ground somehow... Anyway, it's not 5V, so that takes sensors out of the equation.

Sure is looking bad for the PCM. Powers, grounds, then stick a fork in it

Just to confirm, yes it was the green "negative" LED that lit up, while showing .1 volt. I replicated this result three times, cycling the key each time.

Installed the new PCM today, and the car fired right up and ran like a champ. THANK YOU, guys, for your help on this. And scannerdanner, your Cobalt videos really demystified making a call on a bad PCM.

Nice job, thanks for updating us with the fix!

That Cobalt was a good demonstration of how to check a PCM.

popoften wrote: Installed the new PCM today, and the car fired right up and ran like a champ. THANK YOU, guys, for your help on this. And scannerdanner, your Cobalt videos really demystified making a call on a bad PCM.

Sweet! Thanks for letting us know where this one ended up

I still think it's crazy how the Power Probe showed ground on the 5V reference wire... Maybe it got shorted to ground on the board itself? :huh:

Yeah that was a real head-scratcher. But in the end it came down to the PCM getting verified good inputs but some key PCM outputs were garbage. I'm in the software development business, and when we have a "black box" that gets good inputs but gives us bad outputs, we know the problem is in the "black box" somewhere.