My 96 Caravan died and the dealer diagnosed it as the PCM. I had checked it earlier and had come to the same conclusion. He also told me that the coil was bad and that was what killed the coil drivers in the PCM. I had checked the ohms on the coil before taking it in and all had seemed with in specifications.
The dealersaid the trouble codes told him the coil was bad although he hadn't checked the resistance on the coils.

Has anyone seen a bad coil ruin the coil drivers on a PCM or is the dealer trying to make a little extra cash?

 

Yes a short in the coil primary circuit can kill a PCM, but on the early NS caravans the wiring harness that ran under the intake manifold would melt together causing the same kind of short also killing the PCM.

 

Wouldn't a short in the coil show when I did the ohm check on the coil? The primary was pretty much in spec but a little on the high side. All three were consistent though.

I didn't think to look for fused wires.

 

Yeorgos here,
I beleive it is more likely that the pcm circuitry failed on its own. I have traced as much wire as I can and there does not appear to be any shorts for my vehicle. The coil circuitry on the pcb of the pcm has switched many millions of times over for my vehicle, 320 000 km. I would still like to know what comes of your vehicle as I am waiting on a new pcm. If you want to test your pack for actual spark, then there is a method, but it is dangerous.
You would need a condensor (capacitor really), a test light, 12 volts, jumper wire, and two spark plugs mimicing the electrical path they would have in an engine. A lead from both the condensor and test light go to ground. the other lead of the condensor goes to the tip of your test light pen. This mimics the pcm. The 12 volts go to where your Asd or B+ wire would be when the engine is running. You quickly touch the test light to the coil to be tested and there should be spark through the spark plugs. This is DANGEROUS as the voltage induced is ~50 000 volts on a good coil pack. Do only if you are confident in your layout. And don't have a kid hold the plug wires to a good ground, rig up a good system. Also make sure to get a ground for the battery, and make it common with the other grounds. If you want to test the coil like this.
There is a chance that since your lead was always to ground from your pcm it could have overheated the primary coil in that circuit. The ground is only meant to be on for 3 ms or so, and if it is on all the time then it can heat up that .8 ohm resistor or whatever your coil is in there in a hurry.I don't really know, butthe junk yard has many intrepids and other 3.3s withmatching coil packs. Just bring yourmeter and look for ones in accidents.

 

I posted on a similar thread that the dealer has told me that the coil went bad and then killed the PCM. Cost me $800 to replace both. Although the coil did not test bad when I had it the dealer put enough doubt in my head that it may not show a problem until one day it kills the PCM again.

Yeorgos, I've asked for the coil back since they don't offer a core for those. Someday when I'm feeling brave (or foolish) I might try that test.

thanks,

 

Ohms test most likely wouldn't help you in this case, the coil could be leaking secondary HV into the primary windings frying the pcm without there actually being a short in the primary windings. Or an intermittent short in the windings could do the same thing.