Hi, GM vehicles are known for this problem. I'm guessing that when you turn the key, you get nothing, and your security light flashs. If you can, jump the starter, it'll start and run for about 2 seconds and shut down. If you can do that, it will 100% tell you it's your ignition cylinder in your column. But i can already tell you i'm 99% sure thats what it is. And 9 out of 10 of these i have repaired it's not actually the cylinder that has broken. It's a wire going to the cylinder. There are 2 wires that go into the cylinder which are for the resister that is in the key for the PASS system. GM used very small gauge wires for the PASS KEY in the cylinder. Either way you will have to have the column taken apart and have the cylinder repaired.
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Is your key cylinder on the column or on the dash by the column? You dont need to tap the starter. Turn the key to the ON position and use a screw driver and touch the 2 termanals on the starter selenoid together. It should start for about 2 seconds.
if its the ignition, it'll shut off after about 2 seconds on its own.
Use a test light and see if you have voltage at the starter.
Before you go buy a cylinder though. Disassemble it first and look for a broken wire. Here is a breakdown of the procedure for disassembly. Good luck.
IGNITION SWITCH LOCK CYLINDER REPLACEMENT REMOVAL PROCEDURE
In case you need to replace it, here is the procedure for reprogramming.
PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS IMPORTANT:
Conditions Use these procedures after replacing:
10 Minute Learn Procedure TOOLS REQUIRED :None
here is a picture of the starter. You want to use a screwdriver and touch the two threaded rods on the starter selenoid.