Found my way here from LX Forums

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mdnitedx
How the heck did I end up here?
Posts: 4
Joined: 2011 Dec 17 12:04

Found my way here from LX Forums

Post by mdnitedx » 2011 Dec 17 13:05

I wasn't planning on digging into my 2006 Magnum RT for another few months, but an unexpected ECM/PCM issue prompted me to get started sooner rather than later. I've started with an OBD-II interface, however I picked one based on the STN1110 chip...which I think should make for an easy transition to CAN BUS monitoring / hacking once my car's more immediate issues are addressed. Until then I'll just be reading...

I started playing with vehicle bus hacking with J1850 and Atmel micro controllers on Harley motorcycles. Since then I haven't kept up to date with vehicle communications - but I think this community will help me get up to speed. Thanks! :)

mdnitedx
How the heck did I end up here?
Posts: 4
Joined: 2011 Dec 17 12:04

Re: Found my way here from LX Forums

Post by mdnitedx » 2012 May 28 03:03

The PCM issue I mentioned here is now fixed. I'll give a quick explanation.

For the past several months my car has stalled while driving. In the beginning it happened during the warmup cycle on cold (20f) days, either while idling in the driveway or driving on the highway. This was maybe once a week or every two weeks. It ran perfect until it happened, and afterwards the vehicle acted as if nothing had happened (no MIL/CEL, no DTCs*).

With the OBDLink ScanTool I was able to see that things weren't quit right; all of the OBD monitors had been 'reset' and the PCM indicated 0 miles traveled since codes cleared. Here I found another module on the OBD-II interface - I think it is the TCM - and this indicated a different mileage since 'codes cleared'. Infact the TCM showed as having a code logged against the PCM - U0100 / lost communications. This was a soft DTC in the TCM, and the PCM ignored it.

As stalling got worse, I eventually had the MIL light up with a set DTC. This 'said' the PCM detected a TCM error and had generic P0700 transmission codes. The OBD-II freeze frame was interesting; the engine RPM was 0 while everything else was normal. As the stalling got worse, there was some variation in codes and eventually the PCM admitted to a U0100 DTC, but would easily 'stall' again and come up with no DTCs found.

During this lots of things went out..things that the PCM controls. First the motor would stall (and things dependent on having engine RPMs had issues like power steering, power brakes, the AC compressor) - the deceleration was pretty severe. Cruise control would reset to having the light off. Headlights would dim as the alternator control on the PCM went out (the RPMs dropping probably didn't help either). The PCM and TCM would refuse to communicate after some occurrences - I could sit in 'D' with no power delivered because the TCM wouldn't go into gear (never had a 'limp mode' event happen though). Meanwhile other things worked...heated seats, radio, etc.


None of the local dealers (within ~200 miles, that is a population of 1 chain) would diagnose the problem as a PCM issue despite going in with this problem occurring several times. They did offer to start with replacing the TCM for $800+labor before letting me keep it in their shop...but I walked away from that 'deal'. They shot down any mention of 8yr/80000mile federal emissions warranty covering the PCM by saying they wouldn't diagnose my U0100 and P0700 DTCs and drivability issue as a PCM issue and that I would pay for all of the parts they shove into my car trying to fix it (they wanted to start with a $700 TCM + labor). There was also talk of me paying 'their retail' for a new PCM if I ignored their diagnosis with little recourse to be reimbursed if it fixed the issue... I walked out and eventually bought a rebuilt PCM online (~$230 + I ship my old one back). And it works great :)

In short: With those issues behind me, I hope to get hacking soon :)

bettes
How the heck did I end up here?
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Joined: 2012 Mar 29 06:56

Re: Found my way here from LX Forums

Post by bettes » 2012 Jun 01 18:32

good for you. :D alsways nice to read about the stealerships not getting their own way.

mdnitedx
How the heck did I end up here?
Posts: 4
Joined: 2011 Dec 17 12:04

Re: Found my way here from LX Forums

Post by mdnitedx » 2012 Jul 15 19:31

I think I jinxed myself since the problem has reoccured. But my latest change has the car running again - I'm not sure why though.


I built a few simple diagnostic tools/probes to verify power from the battery through the PDC (rear fuse/relay box) to the IPM (front fuse/relay box) and also made some pins to use on the PCM C1 connector plug. Everything seemed to have power as expected, so I began suspecting grounds. They seemed to ring fine as well. I just couldn't check the PCM connectors with the PCM attached.

I almost ordered a Miller 8815 (PCM connector breakout box)...

But I noticed a very strange pattern...whenever I had the PCM out for diagnosis the car ran fine. When I dropped it back into its mounting position the car would stall. So I did my measurements with the plugs in the PCM's mounting cavity - things seemed normal (with my test equipment I can't run the car while ringing the C1 connector). I pulled the PCM connector plugs out to place the PCM in the same upright position as it is in the cavity, but not in the cavity - the car ran fine.

Then I set the wiring up to put it back in the cavity...and decided to set the PCM in with the car running. The car stalled when I set the PCM back in and brought the bolt through the mounting hole. I repeated this a few times...eventually using a metal dental pick...and the car stalled when I touched the body & edge of the bracket with the pick. It happened enough that I decided it wasn't a coincidence, and that movement of the bracket or PCM didn't contribute to this.

So I laid out a few strips of electrical tape where the bracket mounts, taped the upper most threads on the bolt, and made an insulating washer to put under the rertained washer on the bolt so electrically isolate the bracket from the body.


The car seems to run fine now...finished up 2 days of trouble-free operation.

Once the weather clears up and I can ride the motorcycle to work again I hope to figure out what the case is connected to that could be causing this issue...it seems strange that this rebuilt PCM acts this way...and who knows if my original PCM was affected by the same issue?

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