Initial Inspection and Diagnostic Overview

HEATING AND A/C SYSTEM SELF DIAGNOSTICS
All automatic temperature control (ATC) and manual temperature control (MTC) system diagnostic trouble codes (DTC's) are stored in the body control module (BCM). DTC's pertaining to A/C compressor control circuits and radiator fan control circuits are stored in the powertrain control module (PCM). Both systems can be diagnosed by either the DRBIII (R) scan tool or by using the vehicles own diagnostic display system.

NOTE: When using the DRBIII(R) scan tool, refer to the DRBIII (R) menu for DTC listings.

ATC/MTC DTC'S (Part 1):

ATC/MTC DTC'S (Part 2):

ATC DTC'S:

MTC DTC'S:

There are three DTC tables shown. These DTC tables are to be used when diagnosing the ATC and MTC system using only the vehicles diagnostic display. The DTC's cover operation of the climate control door actuators, ambient temperature sensor, in-car temperature sensor, and the A/C-heater control head. The ATC/MTC DTC table contains faults that are common to both the ATC and the MTC systems. The ATC DTC table covers DTC's that only pertain to only the ATC system and the MTC DTC table has DTC's that pertain to only the MTC system.

Climate Control Preliminary DTC Check
1. Clear any DTC's.
2. Operate all HVAC system controls with the engine running at normal operating temperature.
3. Check for any DTC's and perform the required diagnostics if the DTC reappears. Refer to the appropriate Diagnostic Information.

CAUTION: DTC 26 can be created if the in-car temperature sensor is disconnected while the BCM is operating. This can happen by disconnecting connectors from the BCM or the ATC A/C-heater control with the battery connected (even with the ignition switch in the OFF position). To correct, clear DTC 26 from the BCM.

NOTE: Removing connections without disconnecting the battery may generate a DTC. The negative battery cable should always be disconnected prior to servicing any electrical component.

If a DTC does not reappear using the procedure above, check the history of the vehicle for a low battery condition, or ambient temperatures below 4° C (40° F).

TROUBLE CODES FROM THE ATC CONTROL

Entering Self-Diagnostic Mode:

The DTC's can be checked with the ATC control if a DRBIII(R) scan tool is not available. The DTC's are stored in the BCM. The A/C-heater control can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. Set the A/C-heater control to a 24° C (75° F) setting (so there is no confusion with DTCs 23 - 51.

NOTE: It is important that no other control knob or button is pushed until all DTC's are read. Pushing any control button except Panel Mode or turning the blower fan control knob will end the diagnostic test without showing the rest of the DTC's. There also may be other DTC's stored in the BCM not related to the climate control system. These DTC's can only be found using the DRBIII (R) scan tool.

To place the ATC system into diagnostic mode, press and hold the Floor, Mix and Defrost buttons (at the same time). The ATC control display will begin to blink. Release the Floor, Mix and Defrost buttons. Once the A/C-heater control enters the diagnostic mode, the display on the A/C-heater control will continue to blink until it completes an error check and a climate control door calibration. Then it will display any DTC's that are present in the BCM related to the climate control system. If there are no climate control related DTC's, the ATC system will return to its normal operation as indicated by the temperature symbol (C or F). DTC's related to the ATC system will appear on the display in numerical form. The ATC control can only show one DTC at a time. Under certain circumstances, more than one DTC could be in the memory. To scroll through any additional DTC's, press the Panel Mode button on the ATC control.

TROUBLE CODES FROM THE MTC CONTROL

MTC Control Head:

The DTC's can be checked with the MTC control and the Odometer Display of the Mechanical Instrument Cluster if a DRBIII (R) scan tool is not available. The MTC control can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. To place the system into it's diagnostic mode, adjust the MTC control to the following settings:
1. The engine must be running with vehicle not moving.
2. The fan speed set to any speed except OFF.
3. The temperature control knob in full cold (full counterclockwise position).
4. The mode control knob must be placed in Defrost position (full clockwise position).
5. The A/C button can be On or Off.
6. Press and hold the rear window defogger (EBL) button until the mechanical instrument cluster odometer display indicates an "AC00". The BCM will chime once and the MTC A/C button LED will begin blinking.
7. Release the EBL button and wait until the MTC A/C button LED stops blinking. This means that the error check and climate control door calibration is complete.

NOTE: It is important that no other control knob or button is pushed until all DTC's are read. Pushing any button except the A/C button or turning a control knob will end the diagnostic test without showing the rest of the DTC's. There also may be other DTC's stored in the BCM not related to the climate control system. These DTC's can only be found using the DRBIII (R) scan tool.

DTC's related to the MTC control head will appear on the odometer display in numerical form after the letters "AC". The odometer display will return to normal operation if no DTC's are found. If a problem is found, then the odometer will display the letters "A/C" followed by the DTC number. The odometer display can only show one DTC at a time. Under certain circumstances, more than one DTC could be in the memory. To scroll through any additional DTC's, press the A/C button on the MTC control. The BCM will beep each time the A/C button is pushed. Continue pushing the A/C button and recording the DTC's until the odometer returns to normal operation (note the letters AC will disappear).

ERASING DIAGNOSTIC TROUBLE CODES (DTC's)
DTC's can be cleared from the BCM two ways:
- Using a DRBIII (R) scan tool
- Disconnecting the negative battery cable for ten minutes.