Came across a 2009 Silverado 1500 LT 4WD 5.3 Flex Fuel - LC9 motor.
Cheap scanner can't communicate to PCM, code shows U0100. Key appears to be the correct key with that vehicle. Verified all fuses in working order. There was an issue with 1 or 2 fuses not getting power, but stuff was unplugged underneath and that seemed to correct those few fuses (fuel pump related) Purchased a used PCM and had them flash it to match the VIN. Tried taking it to a dealer and 2 weeks later, $200 later they were 0 help as usual. New battery, even bought a used fuse box and threw it in - same issue. Trying to locate all the grounds to be sure there's a good connection as well, just got those locations so I need to check out tonight.

Curious if anyone has had anything similar? I've seen many issues with gauges going crazy and bad PCM issues but does not appear to be the same.

 

Aftermarket stereo?

 

no, stock radio. Works fine when in run position.

 

Did you reset vats?

 

I did attempt to reset VATS. Security light does go away right away. So when I actually attempt to try starting vehicle when in ACC position everything lights up, warning lights pop on regarding stabilitrk and all. When going to start everything turns off and pops back on when releasing from the Run position. Could this be starter? I didn't try to jump off the starter yet, but I still have no communication to the PCU. Only code I was getting was U0100 I believe. Is it possible Ground on back of block is the issue? I haven't gotten to that one yet.

 

As an update- when using jump wire at starter relay I get a crank attempt at least. Short in wires ? ECM to ignition?

 

Nothing?

 

I would think short between ignition and PCM. Nothing is happening when putting the key in the run position so I would follow those wires.

 

How are you reading a U0101 code if the scanner won't communicate with the ECM? I would disable the VATS and Starter Checks with tuning software and see where that gets you.