Hello everyone I have a 2004 silverado 4.3 got tires of the little v6 so I bought a wrecked 2006 silverado 5.3 took of motor, transmission harness resealed engine and put everything on my 2004 now truck won't start I have no pulse I used the 2006 wiring harness computer and ecm fired up once for like 4 seconds and could never get it to start again .😓😓

 

Sounds like a security issue to me. Do you have a tuning software? Try turning off VATS

 

Yep.

If you can't turn off VATS, I would do the key relearn procedure.

 

Or you could have the vin Changed on the 06 PCM so that it matches and will run correctly.