On-Board Diagnostics
Do not exchange A/C Heater Controls from vehicle to vehicle. Software versions differ between models and model years. Installing an A/C Heater Control with software that is incompatible for a given vehicle can result in either improper or failed HVAC system operation.
Always inspect the IOD fuse prior to diagnosing any heating-A/C system concerns. Make sure the fuse is functional and fully seated into the terminals of the totally integrated power module (TIPM) located in the engine compartment.
The A/C-heater control communicates on the controller area network (CAN) B bus and is fully addressable with a scan tool.
The A/C-heater control's primary means of fault detection is through active and stored diagnostic trouble codes (DTCs). Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired in order to clear this type of DTC. Stored DTCs are those which occurred in the system since the A/C-heater control received the last clear diagnostic info message. All DTCs must be read with a scan tool (refer to DIAGNOSIS AND TESTING for the diagnostic test procedures).
The A/C-heater control's secondary means of fault detection is through system tests. These tests include the HVAC System Test, the A/C Cooldown Test, the Actuator Calibration Function, and for MTC Systems, the Actuator DTC Detection Test. Refer to System Tests in this Section for a detailed description of each test.