The heater-A/C control stores Diagnostic Trouble Codes (DTCs) as a 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, the DTC 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 to Intermittents and Poor Connections for more information.

Diagnostic Trouble Codes (DTCs) may 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 information on how to read the following information:

Clear the DTCs after a repair has been completed. Ensure that the scan tool is capable of interfacing with the heater-A/C control before attempting any communications. Connect the scan tool to the Data Link Connection (DLC) and turn the ignition switch to the ON position in order to use the scan tool. The scan tool reads the serial data sent from the heater-A/C control terminal D12 through the splice pack SP205 and then to the DLC, terminal 12.

The scan tool displays the heater-A/C control input status. Select the heater-A/C control status display in order to display the data and determine if the switched inputs can be properly interpreted. The scan tool can also indicate if the input has changed states. For example, when a solenoid control is off, the scan tool displays the output status of the solenoid control as INACTIVE or OFF. When the solenoid control is on, the scan tool reads ACTIVE or ON. Use this type of information when diagnosing a malfunction associated with a particular heater-A/C control input, or an input that is shared with another vehicle system via the class 2 serial data link.

Use a scan tool in order to cycle heater-A/C control air delivery and temperature controls solenoids and motors. This feature may be used in order to determine if the heater-A/C control is able to control a solenoid or motor regardless of the inputs or any specific program instructions. Once a test is selected, the scan tool will command the heater-A/C control to energize the selected solenoid or motor. The displayed information represents only what was heater-A/C control commanded, not if an action has actually taken place. Inspect the heater-A/C control for the ability to control each of the selected solenoid or motor functions through the scan tool.