u/Evening-Blacksmith-6

2018 5.3 Sierra

A while back I was driving on the highway when my truck lost power and would not start. I got it towed home and have since been trying to diagnose it. I am getting codes P0068 & U0100.

I have tested power at my TPS, MAF and some other locations. All is coming back good except I am getting lots of resistance everywhere. 35-40 ohms at all connections and grounds.

I inspected all of the ground cables and wiring harnesses for corrosion or possible problems. All seems fine. I checked the ground inside the cab in the dash as well as removed and cleaned the ground to the chassis from the battery. The ground going to the engine block is a bit hard to access but from what I could see it looks good.

All lights, radio, etc. work, truck just won’t turn over or will die immediately if it does.

Could this be an ecm issue? Any pointers on where to look would be greatly appreciated!

Thank you.

I was on the highway this afternoon when my truck (2018 Sierra 5.3 with 6 speed) randomly entered reduced engine power mode and stalled. It would not even attempt to turn over unless I had the gas pedal to the floor but would not start. I checked the fuses. I removed the air intake and was able to get it to start but it was squealing and stalled after about 30 seconds, would not start again. The throttle body doesn’t look very dirty and moves freely. Could this be a vacuum pump or related issue?

Please help!

Thanks