Self-Diagnostics - HVAC System - Automatic

The heater-A/C control uses information from other Systems in order to deliver information to the driver. Therefore, before further diagnosis, review the general information on how the heater-A/C control system operates and how each system interacts with the heater-A/C control. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.
Use a scan tool to diagnose the heater-A/C control when referred to in diagnostic procedures. In addition to displaying Diagnostic Trouble Codes (DTCs), the scan tool will display the input status and the data values used. The scan tool can also cycle many of the heater-A/C control outputs and indicators both on and off. Any of these features can be selected using the scan tool.
Become very familiar with the heater-A/C control capabilities and diagnostic features. These self-diagnostic features are referenced in the DTC tables and are very useful in diagnosing non-DTC setting malfunctions as well. Notice that not all circuits feeding information to the heater-A/C control will set a DTC if a fault exists within that circuit. Some of these circuits such as the heater solenoid coil output, the heater/defrost solenoid coil output and the recirc solenoid coil output will not set a DTC. Diagnostic tables concerning these circuits are still included to help locate concerns. Refer to A Diagnostic System Check. Diagnostic System Check - HVAC System - Automatic
Replace the heater-A/C control only if the diagnostic procedures specifically direct you to do so. The heater-A/C control does not automatically need to be replaced when a short is found in the wiring. Repair the wiring first, then check the heater-A/C control for further concerns. Most system malfunctions are traceable to faulty wiring and connectors, and occasionally components. The heater A/C-control is very reliable and usually is not the cause of the malfunction. Refer to Control Assembly Replacement