Preliminary Diagnosis

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 computer 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 in order to diagnose the heater-A/C control when referred to in diagnostic procedures. In addition to displaying DTCs, the scan tool will display the input status and the data values used. The scan tool can also cycle many of the indicators and gauges 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. It should be pointed out that not all circuits feeding information to the heater- A/C control will set a code if a fault exists within that circuit. Some of these circuits such as the heater solenoid coil output, the defrost solenoid coil output. the A/C solenoid coil output, the heater/defrost solenoid coil output and the recirc solenoid coil output will not set a trouble code. Diagnostic tables concerning these circuits are still included within this cell to help locate concerns. Performing the heater-A/C control diagnostic system check will help guide a technician to these tables to assist in diagnosis.

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 system 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 not the cause of a system malfunction. A heater-A/C control replacement before a complete diagnosis will usually result in a recurrence of the original complaint.