07 LT 5.3L Sudden no start/crank

Doubeleive said:

@rockola1971 do you know the 12v reference wiring on these from the ignition?

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mikez71 said:

Try another relay yet?

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mikez71 said:

It looks like ignition switch signals BCM through a PINK wire (J1-14)
View attachment 440752

BCM sends relay signal through YELLOW wire (J4-21)
View attachment 440753

Some scanners can tell if your key is in the start position.. Good luck and keep us posted!
I'm not sure the "passthrough" in the diagrams directly passes through or it's just there to show the relationship..

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J-Herkel said:

Getting to the point..
2007 Tahoe LT 197k miles.
Suddenly would not start back up today after running fine for years and even started up 3 times prior today. Battery is brand new, took it out and tested it at the auto store. It's good. Alternator is fairly new. Starter was tested and is good. It will crank with a jumper wire in the relay. Obviously no signal from relay to starter solenoid. Not sure where the sending wire from the starter relay comes from. ECM? Ignition switch? Everything else in the vehicle runs perfect. Radio, lights, power windows, all strong. Just when I go to turn the key over to crank, nothing. And it was sudden. Any ideas?

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Doubeleive said:

@rockola1971 do you know the 12v reference wiring on these from the ignition?

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rockola1971 said:

Im not quite sure what you jumpered in the ignition relay whether it be the control side or the controlled side. Im assuming you jumped the 2 contacts for the controlled side which is what feeds the 12v to the starter solenoid to initiate starter spinning over among other things that happen during that evolution. If not, correct me.
Now as far as the control side of the ignition relay, remember there are 3 things that you need here. (1) Good relay (its coil and contacts) (2) 12v going to the ign relay coil. (3) Ground to that same ignition relay coil. (just had this problem last week from another poster in 2000-2006 section where he was missing ground for the relay).
So here are the schematics involved and the chain of events that happen. (Little bit different from the 2000-2006 chassis).
And the first thing I would check is the main power trigger (Notice I did not say feed) for the control side of the ignition coil which is Fuse 34 2A marked as DLIS. This has to pass through your ignition SWITCH to Plug C1 Terminal 21 of your BCM. The BCM outputs 12v on Plug C4 Terminal 21 directly to the ignition coil relay which if it has a proper ground will energize the internal contacts to close and the starter will begin spinning over and the ignition system and fuel system will all be powered up along with the proper parts of the PCM.

So I would check the Fuse 34 2A DLIS first then if its ok, pull the ignition relay and check the socket for ground for the coil and then have some hold key forward to engine crank position and check the ignition relay socket for 12v at the coil positive terminal.

Let me know what you find or dont find.

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