How do you fix Code P0660 on a Buick Enclave?

Code P0660 on a Buick Enclave indicates a problem with the intake air heater circuit. To fix this issue, first, inspect the wiring and connectors associated with the intake air heater for any signs of damage or corrosion. Next, test the intake air heater relay and the heater element itself for functionality. If any components are faulty, replace them, clear the code, and retest to ensure the issue is resolved.