Jeep PCM problem
Power Control module looses communication with other modules in jeep.
2007 compass it wouldn't crank at all, when i scan it, it says "A communication error has occurred with the ECU", when i scan the tcm its says lost comm with ecu pcm. i got another ecu same thing.
Troubleshooting:
As per problem described it sounds like no modules are communicating with the PCM but it has been replaced with a known good unit?
First make sure all fuses are good. If the PCM loses a power or ground feed that will prevent it from waking up, operating and communicating.
Its suggested to do
load test the PCM powers and grounds.
The procedure to do this would be with a couple jumper wires and a headlamp or fog lamp bulb. The bulb should light as brightly as if you connected it straight to the battery, if it doesn't light or is dim then you know that particular power or ground has a wiring issue.
If you find the powers and grounds to be ok you'll want to check the CAN C bus voltages at the PCM connector, each wire should be about 2.5v with the key on.
If all checks ok but the PCM won't come alive then it could have a short somewhere in the engine compartment that is taking it down. If the sensor ground circuit shorts to voltage (wiring or internally in a sensor) then it could prevent the PCM from waking up, or if a 5v reference circuit shorts to ground it could do the same.
Many a times on such cases you see wire get cut or crimped somewhere loosing the voltage.
So inspect each and every wire visually.
This types of problem sometimes takes long to get solved.
This details will help.
Thanks.
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