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Good morningCustomer my name is Mark
Seems like you have your hands full on this one. Do you have access to a scan tool? I think that would be most helpful in this case.
If your check engine light doesn't work then it won't flash any fault codes for you. You are going to have to test all the powers and grounds going to the computer. When you replaced the PCM, was this new or used.
One other thought, a shorted 5 volt sensor can cause the PCM to shut down. These include the tps, map and crank sensors.......and a few others. Try disconnecting these one at a time and see if your check engine light comes back. You can also test for 5 volts at these sensors and disconnect them one by one until the 5 volts returns. Hope that makes sense to you.
Yes the BCM stores the mileage that is why it stays the same when you change the PCM.
Did you try disconnecting the crank sensor as I suggested and checking for the 5 volt supply voltage.
I understand you seem to be fixated on this "second" computer but unless the communication bus has gone down, it will have zero effect on your no spark, no check engine light.
A shorted sensor causes the computer to shut itself down so it doesn't get damaged......kinda a fail safe mode. Once the short is removed the PCM will be fine.
You stated you didn't have a scan tool but do you have a volt meter?
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