Tahoe starts and dies after 1 second, not security/passcode issue

[Ronjan]

Can someone PLEASE HELP!!!
I have a 2005 Z71 that will not start. It has gas, fuel pressure, spark, signal to fuel injectors, new fuel pump, fuel injectors, rails, lines... It sort of starts for a second and stops. It is NOT the passcode/security as no lights are on. The check engine light is on. I get a signal from odb reader that says communication link failure so i cant get any codes.
It seems like it wants to start but maybe the computer is getting a signal to shut it down. I think its a sensor but really have no idea. Can anyone solve this mystery for me?

 

[Kenny D]

Wonder if it is the computer itself? Check all grounds and connections, it could be possible that once the engine jerks from starting, it breaks a connection somewhere.

 

[ScottyBoy]

I had this SAME issue with my brothers 2001 Tahoe. I dug through all kinds of things and I finally figured it out. It was a bad relay in the under hood fuse/junction box. It was one of the ignition relays. I swapped it with the headlight relay and that sumbitch started right up!

 

[Warriorpluto]

Not sure on that model if you have the ground that's on the back of the passenger side cylinder head. Check it. Check relay as stated. If good then pcm is toast.