Bad Ground Kills Cadillac
This bulletin applies to 2018 and prior Cadillac and other gasoline-powered GM vehicles. Technicians may encounter a concern where the catalytic converter has come apart or has set a P0420 and/or P0430. If you believe the catalytic converter has failed with no apparent reason, it is recommended to inspect for a poor crimp for the coil grounds terminal on the engine block for the bank with the concern. Inspect the grounds for possible corrosion or damage at the ground terminal ring, fasteners and grounding surfaces. If no corrosion or damage is found, tighten the ground bolt to the proper torque.
Examples of corrosion/poor crimps.