Code U0100

Hello,

U0100 - Lost Communication with Engine Control Module.

I would suggest checking 12V supply to the PCM, at connector C1, using a test light
Please see image below for the ignition and fused 12V inputs.
Also, check that both ground connections have good connectivity and no excessive resistance.
First check that the 12V inputs light up the test light bright using a good chassis or engine ground.
Then, using either ground pin 9+18 at the PCM, repeat the test. Test light should light up bright. Ensure that you test both pins!

Next start the engine and let it idle. Once it stalls leave ignition on and check each 12V supply again using the test light, see if any supply has dropped out.

How to use a test light.
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

How to test wiring.
https://www.2carpros.com/articles/how-to-check-wiring

Please let us know how you get along.

Cheers, Boris