Flow of Diagnosis

The Automatic Temperature Control (ATC) system can be diagnosed two ways. The scan tool (DRB) can be used, or the vehicle's own control head display may be used.

ENTERING DIAGNOSTIC MODE
The control head can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. Set the control to a 75°F. setting (so there is no confusion with 23-36 Diagnostic Trouble Codes).

Entering Self Diagnostic Mode:

To place the system into it's diagnostic mode, press and hold the floor, mix and defrost buttons (at the same time). The ATC head display will begin to blink. When the control head display begins to blink release the floor, mix and defrost buttons. Once the control head enters diagnostic mode, the display on the control head will continue to blink. This occurs until it completes its tests and calibrations. Then it will display any diagnostic trouble codes that are present in the Body Control Module (BCM). If there are no diagnostic trouble codes the system will return to its normal operation as indicated by temperature display.

DIAGNOSTIC TROUBLE CODES

Diagnostic Trouble Code Chart:

Diagnostic trouble codes related to the ATC system will appear on the display in numerical form. The diagnostic trouble codes are stored in the BCM and diagnostic trouble code numbers can range between 23 and 36. The control head can only show one diagnostic trouble code at a time. Under certain circumstances more than one diagnostic trouble code could be in the memory To scroll through any additional diagnostic trouble codes, press the panel button.

If diagnostic trouble codes are found, refer to Flow of Diagnosis. Flow of Diagnosis

NOTE: The control head cannot display all diagnostic trouble codes stored with in the BCM. There may be other diagnostic trouble codes in the BCM not related to the ATC system. These codes can only be found using the scan tool.

ERASING DIAGNOSTIC TROUBLE CODES
Diagnostic trouble codes can be cleared from the memory two ways:
- The scan tool
- Power to the BCM can be disconnected for ten minutes (disconnect battery).

CAUTION: Fault code 26 can be created if the sensor is disconnected while it is running; this will result in the control head display disappearing. To correct, clear fault code 26 from the body controller.

Scan Tool Flow Chart:

The Scan Tool Flow Charts are a sample of the areas that be tested with the scan tool. Using the Select System screen press 3 for Body, shows the items that can be tested. Pressing 9 for Climate Control shows the items that can be tested.