On Board Diagnostics
Do not exchange HVAC 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 automatic temperature control system concerns. Make sure the fuse is functional and fully seated into the terminals of the totally integrated power module located in the engine compartment.
The HVAC control communicates on the controller area network CAN IHS bus and is fully addressable with a scan tool.
The HVAC controls primary means of fault detection is through active and stored 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 control received the last clear diagnostic info message. All DTCs must be read with a scan tool.
The HVAC control's secondary means of fault detection is through system tests. These tests include the HVAC system test, the A/C cool down test, the actuator calibration function, and for MTC Systems, the actuator DTC detection test.