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U0100 is set when there is no communication via serial data from the PCM to the other modules in the vehicle. This could happen if:
What kind of diagnostic tools do you have access to?
I'm not familiar with that scan tool. Can it get serial data from the vehicle?
Also, did you make sure the replacement PCM had good power and ground and that it was the right part number for the vehicle and that it was programmed for the vehicle's VIN?
You didn't answer my question regarding your Autel. I don't think I can help you any further if you don't have access to a scan tool that can read serial data from the modules.
Serial data is how the different modules communicate with one another. In your specific case, code U0100 is telling you that the PCM is not communicating with the other modules, which means there is no serial data being received or sent by the PCM. Attached please see the serial data schematic for the 2008 Uplander.
I've never even seen a scan tool such as the one you have, but according to their web site the Autel MaxiDAS DS708 is capable of communicating with all the modules in the vehicle, identify the VIN and even reprogram the PCM.
In your original question, under Already Tried you wrote "Replace the ecm". Just out of curiousity, what diagnostic path led you to replace the ECM?
We're back to the matter of using a capable scan tool to properly diagnose this issue. Other than that, you can check all the powers and grounds going to the PCM to see if something got fried during the jumpstart.
Can you tell me the wire location? Connector and pin number? Are there any other problems with ground and power key off and key on?
So, there are no problems other than circuit 540 not having power?
Glad to be of help. What did you find, a blown 15Amp fuse or a broken wire?