no start on 2012 gmc sierra

[john yazzie]

No start on 2012 gmc sierra 5.3L. put a rebuild motor in and no start now. No communication with scanner on ecm. Gm code u0100-71. Check all my grounds, clean up all my ground connections. and still no start. Anybody knows where I can check next. There's one thing I did when the motor was out was I turned the key on to check the speedometer reading, because that's what they wanted it to know, before I purchase the motor. Would I have grounded my ECM than? Thanks in advance.

[Grubbworm]

I would start with the fuses, check all of them.

I would also check ALL of the relays, with a relay tester. I just dealt with a similar issue with my wife's car. Turns out it was a relay going to an option that was not available on her model car. The relay for the "Bose Speaker/Woofer" was the culprit. I had a U0101 Code, Not communicating with TCM. As luck would have it the CAN (Controller Area Network) also runs through this circuit. Replaced relay and issue fixed. This was not on a GM vehicle, but the principle remains the same.

 

P.S. I got my Relay Tester off Amazon for about $12.

Edited December 14, 2022 by Grubbworm

[swathdiver]

If the cigar lighter has no power, check that fuse first.