Check Engine Light Problem

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ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#12738 Closed 2005 Chevy G1500 Express Van public

Failed Emissions test because Check Engine light (MIL) isn’t working properly. The engine runs fine and doesn’t set any codes. MIL lights normally, key on/engine off, if engine hasn’t been run for a few minutes. Start engine; light shuts off normally. Shut engine off, then try key on/ engine off; the light will not light up. Try again and again, no light. Let it sit a minute or two key off; try key on / engine off and the light turns on. Start engine, light goes out. I’ve repeated this process maybe 50 times over the last few days; same thing every time.
What I’ve done:
• Checked fuses 22 and 31, which the book says power the MIL circuit; both OK.
• Ran engine with gas cap removed to try to force a code set. MIL stayed off.
• Loosened the PCM connectors and wiggled. Everything looks clean and dry. Retightend.
• Removed instrument panel; the connector looks fine. Reinstalled.
• Couldn’t find the G103 ground that grounds the PCM. Book says engine right rear; I’ll keep looking.
The problem is so consistent I’m now thinking something happened to the PCM and that I’ll have to take it to a Chevy dealer to see if their diagnostic machine can find the problem and if it can command the MIL on.
Can you help?
Thanks,
Bill Gray
Sparky

What you are describing is normal function with the exception that all modules may not be turning off quick enough to meet the GM TSB guidelines as listed in the attachment.

Thanks; that’s exactly what it’s doing. I find 20 seconds is enough. I’ll bring the TSB with me for the re-test.

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