Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
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Does the engine crank over and not start or does it not crank over at all? Does the check engine light come on with thek ey on?
Are you looking for possible causes or would you like me to walk you through this diagnoses?
This P0621 code is for an internal failure inside the ECM. YES, it is very likley the ECM is at fault causing this code. However, it may or may not be related to the starting issue you are having. I would check for power at the ignition switch and the complete starting circuit (and ignition switch) to ensure the starting circuit is working like it should before replacing any components.
You can use a test light or a voltmeter to check the starting circuit. I can send you a wiring diagram to help with this. Are you sure there are no anti theft or security lights on or flashing on the dash?
Ok, I would start at the starter relay. Check for two power and one ground going into the relay with the key in the CRANK position. You would do this with the relay removed checking the female pins for voltage. Here is a wiring diagram of your starting circuit.
Sorry, you said it cranks but does not start?
I am sorry about that. Then we need to check for spark and or fuel when cranking. Have you verified that the engine has spark while cranking?
You can use a spark tester or a screw driver. Just gain access to the spark plug wire and remove it from the spark plug and insert the spark tester. YES, if there is no spark and all fuses are good, it could be a bad ECM.
YES, they are pretty close. One controls the transmission and the other one does not. Yours is actually a PCM.
Ok, then it is the ECM
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