How to ACTUALLY Reset the PCM or TCM

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Cadillac STS-V Series Forum Discussion, How to ACTUALLY Reset the PCM or TCM in Cadillac V-Series Forums; Just wanted to share some information that I learned at the dealer this past week. Contrary to some posts I ...
  1. #1
    BlownV is offline Cadillac Owners Fanatic
    Automobile(s): 2011 CTS-V
    Join Date
    May 2010

    How to ACTUALLY Reset the PCM or TCM

    Just wanted to share some information that I learned at the dealer this past week.

    Contrary to some posts I have read on here that pulling the battery terminal off for a few hours or even overnight will reset the PCM and TCM to clear the 'learned' characteristics, this is not the case. I was under the impression that this worked and even tried it to fix a TCM issue I was having. I thought I had fixed the issue when I pulled the battery overnight but the problem came back a few days later.

    After a trip to the dealer and a long conversation with their technical service manager (someone who knew what they were talking about and could keep conversation with me at an engineering level) I found out that the capacitance is on the order of several days to a week. So unless you want to avoid driving your car for a week this is not a solution.

    You can either take the car to the dealer to have them access the PCM and TCM to reset all of the 'learned' parameters or dive in with EFILive.

    Either way...just sharing some useful knowledge.

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  3. #2
    CMNTMXR57 is offline Cadillac Owners Connoisseur
    Automobile(s): 2006 STS-V, 2004 Pontiac GTO, 1999 Chevrolet Suburban LT 4x4
    Join Date
    Feb 2009
    In a GM Service Dept

    Re: How to ACTUALLY Reset the PCM or TCM

    Actually, resetting it via postive terminal removal WILL put it into Idle-Relearn mode. It's akin to re-booting your PC. So yes it DOES reset your PCM. If your problem came back a few days later, there is a problem elsewhere, like a glitch in PCM calibration you have, faulty sensor, faulty wiring harness/connectors/etc, or even some other mechanical issue at hand that is causing the problem. Another option to do an idle-relearn, which I haven't looked into on this car due to time, is turning on your accessory option with the push button start, and removing your PCM IGN fuse, then the PCM BAT fuse (if we have them in the underhood electronic center). let it simmer for a few minutes, shut the accessory off, and reinstall the fuses.

    BTW, I'm a former GM Tech, and do both of these tricks on any GM vehicle that has needed it, including my own.

    And a side note, I've done this on my V several times. I actually do it at every oil changes to clear it of any "bad" learned driving habits. A couple times I've had to do it was because when I hooked up my Tech 2, through the CANDii module (which I believe is faulty), it sent the PCM into a tizzy, sending all gauges into freak out mode and locking the brakes, making the car drive around like it had the parking brake on. A quick idle-relearn by removing the positive terminal of the battery resets it, and puts everything back to normal (and into idle-relearn mode). I will also do it when I get my Spectre CAI so that the PCM learns the new incoming airflow and airspeed parameters this intake allows.

    The Service guy you spoke to pretty much fed you the B.S. we're supposed to tell you, so you don't go poking around under your hood, pulling random fuses, battery terminals, and other shit, which could cause potential voltage spikes, shorts, or other issues, that you then had to bring to us to fix. We then find out you tried to fix the problem yourself and deny you coverage on your warranty since it was a self-induced problem, causing you to have to pay for our time to troubleshoot the electronics and wiring harnesses to find the problem, which isn't cheap. It's not like finding a coolant or oil leak and fixing it. You can't see electricity in wires... So it's really to protect you from yourself.

  4. #3
    BlownV is offline Cadillac Owners Fanatic
    Automobile(s): 2011 CTS-V
    Join Date
    May 2010
    Thread Starter

    Re: How to ACTUALLY Reset the PCM or TCM

    Hm...well that is interesting. Speaking in strictly EE terms, if the PCM and TCM are truly being powered for these extended durations by a capacitor then unhooking the positive or negative or both terminals from the battery should have no effect on the discharge duration. In either case you have removed the voltage potential being supplied...1/2cv^2.

    At least speaking directly about the TCM since I have not delved into the PCM, when I unhooked the battery (both terminals) overnight it did not fix my problem which was embedded in the TCM. Also, using EFILive I noticed that the ramp rate settings and learned characters were still stored until the dealer reset the ECU for me. At that time the issue went away. Also, they tried to use their Tech2 to figure out what was wrong and they were stumped although they admitted there was certainly a problem.

    For what it is worth I was also once a tech, although not GM and I have had to do some relearning but I got lucky in that my coworker's dad is the technical service manager I spoke I hope there wasn't too much BS going around or things will get sticky.

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