Automatic Temperature Control (ATC) Systems

Diagnostic Trouble Codes (DTC's)
The ATC system is controlled by the Body Control Module (BCM). The system can be diagnosed by the DRB scan tool or the vehicles own control head display. Refer to Displaying and Reading Trouble Codes for checking Diagnostic Trouble Codes (DTC's). Note that there are two DTC tables. The ATC and Manual A/C DTC table contain faults that are common to both the ATC and the Manual A/C system. The same diagnosis can be used for both systems. The DTC's cover operation of the climate control unit actuators, doors, evaporator temperature sensor, ambient temperature sensor and the A/C refrigerant system. The ATC DTC table has DTC's for ATC Head Communications, In-Car Temperature Sensor and Sun Sensor which are not in a Manual A/C system.

ATC And Manual A/C DTC'S:

ATC DTC'S:

Entering Self-Diagnostic Mode:

Trouble Codes From The ATC Control
The trouble codes can be checked with the ATC control if a DRB scan tool is not available. 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 the 23-51 Diagnostic Trouble Codes (DTC's).

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. Release the Floor, Mix and Defrost buttons. Once the control head enters the diagnostic mode, the display on the control head will continue to blink. This occurs until it completes its tests and climate control unit door/actuator calibrations. Then it will display any diagnostic trouble codes that are present in the BCM. If there are no diagnostic trouble codes, the system will return to its normal operation as indicated by the temperature symbol (a C or a F). Diagnostic trouble codes related to the ATC and climate control unit will appear on the display in numerical form. The diagnostic trouble codes are stored in the BCM and can range between 23 and 51.The ATC control 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 Mode button on the ATC control. It is important that no other knob or button is pushed until all codes are read. Pushing any button except Panel Mode or turning a knob will end the diagnostic test without showing the rest of the trouble codes. There also may be other trouble codes stored in the BCM not related to the Climate Control System. These codes can only be found using the DRB scan tool.