The heater-A/C control stores Diagnostic Trouble Codes (DTCs) as current or history DTC. If the heater-A/C control detects a system malfunction, the heater-A/C control will only store a DTC that corresponds to that particular malfunction. If a current DTC is stored and the fault is no longer present, some DTCs will remain current until the first ignition cycle. Other DTCs will go into history when the fault is no longer present and does not require an ignition cycle. The history DTCs are intermittent malfunctions and must be diagnosed differently than current DTCs. Refer Intermittents and Poor Connections for more information.

Diagnostic Trouble Codes (DTCs) can be read through the use of a scan tool. There are no provisions for flash code diagnostics. Refer to the scan tool manual for specific directions or instructions.

The scan tool provides this information:

Clear the DTCs after a repair has been completed. Make sure the scan tool is capable of interfacing with the heater-A/C control before attempting any communications. To use the scan tool, connect the scan tool to the Data Link Connection (DLC) and turn the ignition switch on. The scan tool reads serial data sent from the heater-A/C control terminal D12 through the splice pack SP205 and then to the DLC terminal 2.