2005 Dodge Grand Caravan SXT 3.8L. I need some info on why my PCM fried. History: Over the past year my van has had some missing issues. Primarily at startup. One code was reoccurring, misfire cylinder 3. Last week I went to a local town 15 miles away. While parked with the engine running it just all at once started missing very badly and the check engine light started flashing. Probably not the thing to do but being strapped for cash I tried to get back home. I had very minimal throttle responce but it managed to get going with the pedal almost to the floor. As I continued on at times it would buck and gradually I lost all engine power and stalled. It would crank but not start. Got a tow home and ran codes. Misfire cylinder 3, random misfires, all 3 coils in the pack, number 6 cylinder and TP sensor. Due to the lack of throttle response I diagnosed the TP sensor. All in specs. I replaced the coil pack and plugs. Still no fire. I checked for ignition pulse going into the coil pack, nothing. So I replaced the Crank Sensor, still no pulse. On further inspection I found that my ASD (auto shut down) fuse was blown. I replaced it and the engine tried to start but blew the fuse again. So I went wire hunting for short to ground. Nothing obvious. I again replaced the fuse and it just popped this time before engaging the starter. But now my radiator fans came on with the ignition off. PCM? So I pulled tire and inner fender and I could smell the burnt electricity. Upon opening it up the whole top half of the mother board was fried. All the chips were burnt and the heat gel had burnt away exposing the board. Now my question. What caused this? I've done a very thorough wiring and harness inspection. But could a coil pack or alternator failure or something else cause this much destruction? I don't want to fry my new PCM thats coming. Any body have this happen? Can a PCM just burn up? Thanks for any input

All the gel has burnt away

The upper gel is still intact.

 

This type of damage could only be caused by a direct short to voltage in which the board itself became the load. Most likely it’s within the wiring harness (as opposed to an internal PCM short).

1) Disconnect the battery if you haven’t already.

2) Check the fuse box for fuses or relays that are clearly blown or damaged (melted terminals) and inspect the PCM connectors for tracking (dark sooty spots) between the terminals - if present, these will tell you which circuits are responsible for the short.

3) Check the wiring harness for indicators of heat damage (melted loom) or chafing (any area resting directly against the engine is most likely to have chafing). If you see these, open the harness in that area to inspect for damaged wires.

 

Thanks for responding. I have to agree with your thoughts. It would seem visible electrical shorts in the PCM connector, fuse block mother board, coil pack connector, alternator connector...something would show signs of voltage overload. but I see nothing. With that much internal damage to the PCM you would think at least one of the 4 PCM connector leads would show signs of overload with melting or visible damage, but no. That's what's killing me. Everything I've inspected is in perfect condition. I really want to see some damage somewhere before putting in my new PCM. But it all seems to be contained in the PCM. I'm heading out to do it all over again to 100% verify my findings, and I need to see something to warrant the damage done to the PCM. But not to dismiss your advice or lead you into my thought pattern, and not knowing if a PCM can self destruct, I was given warning to what happen. Over the last year or so the van has exhibited missing issues with no clear fix. It progressed even with new plugs, wires, coil pack and inspection of the EGR valve, noid testing, injector harness inspection, compression and vacuum testing. All with no improvement to it's missing issues. It even got worse with occasional random bucking in time. Which I attributed to the transmission being she has just over 200000 miles on her. And the way it went from a slight miss to bam, almost complete failure while just parked and idling. Then I finished it off with my attempt to get her back home. And she gave it her all to try and make this happen. And the bucking became very clear as she did. Do you think it's possible that a PCM could just self destruct internally given the last 10 miles of abuse I gave it? Or do I have to find a source of it's demise. As bad as the internal damage is I'm baffled that one of the male connectors to the PCM wasn't melted to female connector. Been wrenching over 30 years. This ones got me stummped.

 

It’s absolutely possible this is the result of an internal short - I just wouldn’t be willing to name that as the cause until the wiring is definitively ruled out.

I agree the lack of harness damage is interesting, however, it takes lower temperatures to melt plastic than it does brass or copper. Also, if there is a short in the harness, it may not have melted the loom depending on its location (if the short is centered in a bundle of wires as opposed to being closer to the loom, for example).

Don’t forget to also inspect the wiring under the driver side dash and steering column area, as there’s at least 1 ignition switch feed to the PCM.

By chance, are you using any fuses purchased from Harbor Freight (that you’re aware of)? I don’t remember exactly when it was, but some years ago, Harbor Freight fuses were found to be defective and wouldn’t go open when they were supposed to, allowing this type of severe electrical damage to occur. I haven’t looked recently, but for at least a few years after that, manufacturers were issuing bulletins about denying warranty claims if those fuses were found to be at fault. I don’t know what/if HF did to correct the problem. I’d recommend replacing them if you have been using them, or if you’re not sure.

The next step should be testing the power and ground circuits for the PCM. I would use an incandescent test light with a low amperage fuse in the circuit (5A or less). If it won’t work on 5A or less, try 10 - use the battery to check before you start circuit tests.

And on that note, make sure the battery and alternator are good as well. Take the alternator to a shop that specializes in auto electric systems - they’ll test it much more thoroughly than a parts store. It’s possible the alternator has a short and started sending excessive current into the system.

Do you have a wiring diagram?

 

Yeah, I did see one area of concern in the loom where it goes through the fender behind the battery. I'll open up all the areas that make contact like over the bell housing and such. Never thought of the wiring under the dash, thanks. I already have the alternator off to take to napa for testing. I'm in the sticks about 150 miles from any major city. And my second vehicle is a bit tired. I hate to push her over the edge also. As far as circuit testing I'm pretty limited on info but getting little bits here and there on the web. Electrical work is my weak point dealing with autos. To be honest, I dread it and avoid it as much as possible. So many variables sending you in all directions for a fix. I just have basic tools for tracking so I follow the DTC's chipping away looking for the cause.

I really appreciate your giving me your time in this matter and some direction. Your awesome. Anything else comes to mind let me know. Sure would love to see some open copper or compromised wires somewhere. Been racking the web for more info. An Alldata account would be sweet right about now.

Fingers crossed, Thanks

 

I told you not to leave an open bottle of nitric acid on your PCM!

 

I’ve been trying since yesterday to come up with a response to compliment that, but I just couldn’t. Bravo, ol’ chap...

Back to the OP and circuit testing - the checks that need to be done on the wiring are all power and ground circuits and can be done using a test light to start with.

The diagram below is a pin out of the PCM connectors - this one specifies C1, but the others are all set up the same way. The view is of the connector face. Just hook your test light to the positive or negative battery terminal as necessary and touch it to the corresponding connector terminal to complete the circuit. Test light on = good circuit. Test light off or glowing dimly = open or high resistance.



C1 and C4 are the 2 with primary power and ground circuits - I added C2 and C3 for later reference if needed.

C1 grounds are pins 9 & 18.
Power feeds are:
Pin 11 is an ignition switch feed so make sure the key is on.
Pin 29 is a direct battery positive feed.

C4 only has 2 grounds on pins 13 and 14, no power feeds.

ALL the grounds for the PCM are spliced together within the harness and ground at G101 which is near the starter.

Post your findings and we’ll see where to go from there.

 

Yahooooo...After a fun filled day Friday, literally opening every loom and bends and contact surfaces. Dissecting the fuse and rely box. Verifying all my primary grounds. Nothing. Not one burn, melt, exposed wires, having the alternator load tested, nothing giving me a clue on what fried the PCM. I had bought a used one off of ebay, yeah I know, that's scary. But with 100% feedback I took the plunge. Module Madness, awesome folks who got me my pre-programmed PCM in two days at no extra charge. I was sure I had missed something and was sure I was about to toss $180. out the door when installing it. Or my key wouldn't communicate with the PCM and all kinds of other horror stories I had read about used PCM's. But I think we won. She fired back to life. Hell Yeah! 2 days now and she's doing great.

I just wanted to let you know about our victory and can't say how much your input is appreciated, no lie my friend. Thank you. Your awesome.

Be well