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.
The HVAC Module communicates on the controller area network (CAN) B bus and is fully addressable with a scan tool.
The HVAC Module'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 HVAC Module received the last clear diagnostic info message. All DTCs must be read with a scan tool.
The HVAC Module'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.