A little help with my son’s 2003 Tahoe

[Fless]

Is it your understanding that the OP has good power waiting to get the fuel pump at the relay contacts since it works when jumped. No Starter action whatsoever. This is ALL control side problem in the ignition circuit or PCM since he is NOT getting fuel pump relay closure and starter S terminal is not getting 12v likely either. OP seems overwhelmed and cant keep from jumping around which is just further confusing him. If he would just stay on track and do some simple voltage checks this will likely turn out to be 2hrs tops to figure out the cause.

Yes on the fuel pump control missing is my thought; at least that's the view I'm getting.

I'm not really quite sure about the starter issue, which is why I suggested bypassing the starter relay. If the starter cranks when doing that, it's totally a control issue, as you've noted.

 

[Ash4l]

Ok. I took half the day off to try and trouble shoot it and it started right up.

Could it be the security system causing it to lock itself out?

 

[Fless]

The OE security system will allow the engine to crank and start, but if it's in play it won't run more than a few seconds.

If there's an aftermarket security system on it, all bets are off.

 

[Ash4l]

Hmmm. It did something like this once before. A few months ago. Due to another part busting last summer, he filled the radiator up with water to get it home. He never drained it and filled with antifreeze. We had a cold snap for a few days a few months ago and it wouldn’t crank. Changed battery and thought it froze up but the radiator plug wasn’t blown out. Then magically 5-6 days later it started. Just like this time.