GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hi, I am Mike, welcome. I'm reviewing your question.
Try this. Hold the key on start while you move the shifter from park all the way to low and back and forth a few times while holding the key on start. Does at any time the starter catch?
Ok, that was just a test to see if maybe the neutral switch was the problem.
Is this the Sierra? If so, which engine dies it have in it?
Are you familiar with where the fuse box/s are and specifically the starter relay?
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Go to that underhood fuse block, then tell me if the "IGN A" fuse is not blown.
If all the fuses are just numbered, than it's #3.
Ok, great. Now do you have a voltmeter or at least a 12 volt test light? If so, test both sides of that fuse for voltage with the key off.
Then put your finger tips on the starter relay and have someone turn the key to start and tell me if you can feel that relay click.
Ok, do you want to wait until you have someone to help you?
Well, you could try this and it should only cost $10 or so. Replace all the fuses associated with that starter and also replace the starter relay. The fuses are that fuse you just checked the IGN A and the IGN C in that same underhood fuse block. Then there is the CRANK fuse in the left I/P fuse block, that is located at the left side of the instrument panel. If it still is doing it, then you may be looking at a faulty park/neutral position switch which is on the transmission. It sounds like that may be it too since you did say sometimes moving the shifter does help it crank over.
The crank fuse is #17.
Here is the wiring diagram I was looking at,
Don't forget to rate me well, so I get credit especially if changing any of those fuses or starter relay does get the starter working, if not, I understand.