SureTrack Community Fix: Ratchet Drop

Real Fixes from the SureTrackĀ® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-onĀ® diagnostic software version.

Having an tool accident while working on a customer’s car can lead to big issues. SureTrack community member Richard_C had a GMC Envoty in their shop for a head gasket change and when the tech was done, they accidentally shorted the battery and then the truck wouldn’t start. They posed the question to the community, and with the help of fellow community member mwk6503 and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

2002 GMC Envoy 4.2L

No crank, no start, fixed PCM ground.

No start.

Diagnostic Steps Performed/Parts Replaced
Vehicle was in for leaking head gasket. After head gasket install, the technician let his ratchet drop and shorted the battery positive and negative terminals. Car will not start, no cranking. Found the main fuse (125A) blown and replaced it. Tested the starter relay (good) and was able to trigger starter at fuse box but found missing signal was ground signal to the relay from PCM. Checked all fuses to PCM. Decided to just buy reman PCM (inexpensive). Went through relearn VTD procedure. Security light now off, but car will still not start/crank. Suspect ignition switch? Also, when starter is triggered at relay with key in on position, continuous cranking will still not start car.

Also, strange but no Service Engine Soon light is to be found when ignition is on. No related issues scanning all modules. No codes found in modules related to start. Just like A/C etc. or ONSTAR faults. Did look at live data and see ignition 1 and 3 (no 2 option) if I recall correctly. 1 and 3 show on when key is in on position. Ignition #3 goes to “off” when key is turned to start. Possible ignition switch? GMC is not my wheelhouse so any advice would be appreciated on what to look for.

Turned out the ground to the PCM was bad. What was confusing was that I could always scan the PCM and even observe live data. I watched throttle position percentages move and even saw RPM data when cranking. However, there was no ground signal measured at the harness from the source side of the engine. Wonder why I was able to read PCM data without grounds (only two pins into the PCM originating from the same source)? Possibly, the PCM was taking it from somewhere else but with very low current. Either way, just cleaned the PCM ground source, and the starter turned over, CEL was on in run position with the engine off, and the engine started.

PCM ground was bad even though scanner data was operational

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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.