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sprinkles08, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 23118
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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I have a 2004 Cadillac CTS 3.6l I accidently touched the

Customer Question

Customer: I have a 2004 Cadillac CTS 3.6l I accidently touched the opposite end of the top or hot end of the battery cable to the body of the car while trying to reconnect that end to fuse/relay box and a flash. My ingnition will not click when I turn the key and the instrument panel will not light up. The DIC says two reading "service AC and Service air bags". The OBD code is U0100. Lost communication with ECM/PCM A?
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Submitted: 1 year ago.
Category: Cadillac
Customer: replied 1 year ago.
I found one fuse bad, 20, I/P PANEL ACCESSORY PANEL POWER OUTLET. When I pulled another fuse out the flashers began flashing except for the left front turner signal light on front of car.
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

Damage to multiple modules was almost certainly done. The U0100 sets in a module when that module isn't communicating with the powertrain control module. The PCM is the module that controls all engine functions and it not being operational is the reason the engine won't start.

If all fuses are good then the next step would be to test the powers and grounds at the PCM to make sure they're present, and then it can be condemned. Wiring problems almost surely wouldn't have resulted from the polarity issue, so if fuses are good then there is little chance the PCM hasn't failed.

An actual scan tool would be needed to further diagnose the rest of the problems. The other warning lights may be on because the PCM isn't operational but they may be separate issues, for instance the airbag module may have also failed. If these other warnings are present after the engine is running again then an actual scan tool will need to be used to see if the airbag module and a/c control head are communicating.