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    Thread: What a flakey relay 109 looks like to the TCM

    1. Junior Member Matt_TDI16V's Avatar
      Join Date
      Jan 3rd, 2009
      Santa Maria, CA
      97 Jetta GLX TDI swap
      09-21-2010 06:42 PM #1
      5 Faults Found:

      00518 - Throttle Position Sensor (G69)
      16-10 - Signal Outside Specifications - Intermittent
      00660 - Kickdown Switch or Throttle Position Sensor
      27-10 - Implausible Signal - Intermittent
      00529 - Engine Speed Signal Missing
      35-00 - -
      00545 - Engine-Transmission Electrical Connection
      31-00 - Open or Short to Ground
      01314 - Engine Control Module
      49-00 - No Communications

      This is from a '99.5 Golf I looked at last week. The car died while driving and also had been stuck in the transmission's limp mode (only forward gear is 3rd) for sometime.

      One local shop regarded to be good with TDIs told her she needed a new 01M transmission.

      170,000 miles on car and transmission, but it had seen reasonably regular fluid changes/maintenance.

      When I showed up, the car had trouble starting due to a weak battery. After a jump, it fired up, no problems. No codes stored in the engine computer, but the above codes appeared in the TCM.

      I cleared them, see if any would come back. None came back right away. I cleared the adaptations in the TCM and went for a test drive. Transmission engaged every gear as it should. No surging or other signs of imminent 01M death.

      The car drove as it should!

      The owner shuts it down, mystified that none of the symptoms she had described to me were occurring in my presence. Tries to restart it again and it would only crank. No start.

      OK, so I don't think there's any problem with the transmission side of things!

      I'll spare you the rest of the details of me chasing my tail (trying many possibilities that aren't the relay 109 because I had been told it was replaced ). At one point I'm in the car looking at a few things, starting and restarting the car, just cycling the key, I finally get to where it wouldn't start again.

      I cycle the key a few times, watching the CEL and GP lights come on, and finally notice during one of those cycles that the CEL and GP light never come on. AH HAH! Gotta be that 109.

      Sure enough, the same codes as above reappear (this happens after every time it would crank but not start).

      I could cycle the key many times and one out of every 8 or so tries it wouldn't power up the ECM (no CEL and GP light) and the same codes would appear. Clear the codes again, shut the key off, this time remove the 109 and key back on. Sure enough, same codes in the TCM.

      Get my hands on a good 109 and cycle the key many more times just to make sure it powers up the ECM every time. It does.

      Looking at all those codes initially made me suspect the 109 because they all relate to engine control components the TCM needs to see but intermittently couldn't. What do all those components have in common? They all certainly can't be going bad at the same time. Need to look for a common power or ground that's causing issues and that happens to be relay 109 in this instance.

      Interestingly, her generic OBDII scantool came up with a P0725 code--vehicle speed sensor. Meanwhile there's no VAG-specific code in the ECM, just codes stored in the TCM. Though the 7 in the code does denote transmission, the code doesn't help much. There are 3 VSSs on an 01M, 2 of which could cause the transmission to go into its own limp home mode (3rd gear). The 3rd being for the ECM/instruments. Without the extra VAG-Specific codes to let me know there's a general intermittent communications issue with the ECM, TPS and other engine-sensors, I could have been chasing my tail even longer on this one!

      Yet another reason to get VCDS over any generic OBDII thing

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    3. 09-21-2010 10:29 PM #2
      Nice catch! Ill keep this one in mind!

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