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2008 trailblazer. 4.2. PCM is intermittently not grounding starter relay. When turning key to crank nothing will happen. After turning ignition from off to crank multiple times it will finally crank over. Unpredictable when it will/won’t crank.

  • replaced PCM (still happening)
  • new ignition switch
  • new starter relay
I printed off starter relay wiring diagram and tested.

- pin 86 hot with key on
(IGN-E fuse 22 good, and PNP switch functioning correctly.)
  • pin 87 always hot (IGN-A fuse 34 good)
  • pin 85 intermittently not being grounding by pcm. (Replaces pcm and still occurring)
  • purple wire to starter hot when pcm decides to ground pin 85.
  • can hot wire starter relay and starter will turn over fine.
can hot wire starter itself and will turn over.
  • continuity from IGN-E fuse 22 at PCM
  • continuity from CRANK fuse 17 to PCM
Not sure why the NEW pcm is doing the same thing. Is there a grounding diagram available? And I can check and clean all grounds. Any suggestions would be greatly appreciated. Thank you!!
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