Initial Inspection and Diagnostic Overview
ON-BOARD DIAGNOSTICSCAUTION: Do not exchange A/C-Heater Controls from vehicle to vehicle. Software versions differ between models and model years. Installing an A/C-Heater Control with software that is incompatible for a given vehicle can result in either improper or failed HVAC system operation.
SETTING FAULTS - ATC AND MTC SYSTEMS
Both the automatic temperature control (ATC) and the manual temperature control (MTC) systems are controlled by the A/C-heater control located on the center bezel of the instrument panel. The ATC system communicates on the controller area network (CAN) B bus and is fully addressable with a scan tool. The MTC system is NOT connected to the CAN bus and is NOT addressable with a scan tool.
The A/C-heater control's primary means of fault detection for both heating-A/C systems is through active and stored diagnostic trouble codes (DTCs). The control continuously monitors various internal parameters during normal system operation. If it detects a fault, both an active and a stored diagnostic trouble code (DTC) will set for that parameter. When the offending parameter returns to an acceptable value, the control automatically clears the active DTC. However, the stored DTC remains until cleared (either manually or automatically). Note that DTCs will not set or clear if supply voltage is low.
The A/C-heater control's secondary means of fault detection for both heating-A/C systems is through system tests. For ATC systems, these tests include the HVAC System Test, the Cooldown Test, and Actuator Calibration. For MTC systems, these tests include the HVAC System Test, the Cooldown Test, Actuator Calibration (new MTC installation only), and the Actuator Circuit Test / Door Calibration Function. Refer to System Tests for a detailed description of each test.
The Rear HVAC system is controlled by the Rear A/C-heater control located in the rear of the vehicle and by a switch in the Upper Switch Bank located on the center bezel of the instrument panel. The Rear HVAC system is NOT connected to the CAN bus and is NOT addressable with a scan tool.
DISPLAYING FAULTS AND READING FAULTS - ATC SYSTEM
Use a scan tool to display DTCs stored in the A/C-heater control of the ATC system.
DISPLAYING FAULTS AND READING FAULTS - MTC SYSTEM
Use the A/C-heater control to display DTCs stored in the A/C-heater control of the MTC system. Refer to Entering Display DTC Mode - MTC System; Display Sequencing - MTC System; Reading Diagnostic Trouble Codes - MTC System; Active DTCs - ATC and MTC Systems; Stored DTCs - ATC and MTC Systems; and Clearing Faults - MTC System.
ENTERING DISPLAY DTC MODE - MTC SYSTEM
To enter the MTC system's Display DTC Mode, perform the following:
NOTE: An active DTC 33 will prevent the control from entering diagnostic mode and performing certain diagnostic functions. It will also prevent proper A/C mode switch and status indicator function. If this occurs, refer to A/C HEATER CONTROL WILL NOT ENTER DIAGNOSTIC MODE (MTC) for the diagnostic test procedure. A/C Heater Control Will Not Enter Diagnostic Mode (MTC)
1. Turn the ignition to the On position.
2. Turn the blower motor control (1) to the On position.
3. Press the A/C mode switch (2) down, turn the blower motor control to the Off position, wait until both LEDs illuminate (approximately 5 seconds) and then release the A/C switch. If there are active or stored DTCs to display, the A/C status indicator (3) will begin to flash. If there are no active or stored DTCs to display, the LEDs on the A/Cheater control (4) will turn off and the system will automatically exit the mode of operation.
4. To manually exit Display DTC Mode, either turn the ignition off or disconnect the negative battery cable from the battery.
DISPLAY SEQUENCING - MTC SYSTEM
MTC system DTCs will display in ascending numerical order but not in chronological order. Active DTCs will display before stored DTCs. If there are active and stored DTCs for the same parameter, the A/C-heater control will NOT display the stored DTC for that parameter. The EBL status indicator will illuminate and remain illuminated while the A/C-heater control is displaying stored DTCs. After displaying all active and stored DTCs, the A/C-heater control restarts at the beginning, displaying all DTCs again. To restart the sequence from the beginning while the A/C heater control is displaying DTCs, press the EBL mode switch down, and then release it. This will cause the A/Cheater control to quit displaying the present code, turn off all LEDs for 2.0 seconds, and then it will begin flashing all DTCs again from the beginning.
READING DIAGNOSTIC TROUBLE CODES - MTC SYSTEM
All active and stored DTCs for the MTC system have an assigned code number. The A/C status indicator flashes in a series of pulses to display the code numbers. Each pulse has an indicator on time of 0.5 seconds. The tens unit value (1) is flashed first followed by the ones unit value (2). A 2.0 second indicator off-time (3) separates the unit values. When displaying multiple DTCs, the A/C status indicator will go off for five seconds (4) before displaying the next DTC (5). After displaying all DTCs (6), the sequence will repeat until exiting Display DTC Mode.
ACTIVE DTCS - ATC AND MTC SYSTEMS
Refer to Electrical Diagnostics to diagnose HVAC system DTCs.
STORED DTCs - ATC AND MTC SYSTEMS
The HVAC System Test, found HVAC - Electrical Diagnostics, provides a means for diagnosing stored DTCs. The HVAC System Test consists of multiple diagnostic procedures which cover:
- A/C System Performance
- System Controls
- Air-door Functionality
Either perform the entire diagnostic procedure for a complete system test or perform an individual procedure if diagnosing a specific symptom, condition, or DTC.
CLEARING FAULTS - ATC SYSTEM
For every fault that sets, the A/C-heater control maintains an independent count of the number of key cycles since the active DTC cleared, the odometer reading when the DTC set, and the elapsed ignition on time that the DTC was active. When the number of key cycles (by parameter) reaches a global number, the system automatically clears all of the information associated with that DTC. A loss of battery voltage will also clear all active DTCs and associated data from memory. However, upon reconnecting the battery and activating the A/C-heater control ("Ignition" line going "HIGH"), the system will again evaluate all parameters and will set active DTCs for parameters outside of acceptable limits.
DTCs can also be cleared manually from the A/C-heater control (which also resets key cycle counters). Use a scan tool to clear DTCs stored in the A/C-heater control of the ATC system.
CLEARING FAULTS - MTC SYSTEM
To clear DTCs stored in the A/C-heater control of the MTC system, perform the following:
NOTE:
- An active DTC 33 will prevent the control from entering diagnostic mode and performing certain diagnostic functions. It will also prevent proper A/C mode switch and status indicator function. If this occurs, refer to A/C HEATER CONTROL WILL NOT ENTER DIAGNOSTIC MODE (MTC) for the diagnostic test procedure. A/C Heater Control Will Not Enter Diagnostic Mode (MTC)
- An active DTC 34 will prevent the control from performing certain diagnostic functions and it will prevent proper EBL mode switch and status indicator function. If active, diagnose and repair DTC 34 before proceeding. Refer to HVAC Electrical Diagnostics for the diagnostic test procedure.
1. Turn the ignition to the On position.
2. Turn the blower motor control (1) to the On position.
3. Press the A/C mode switch (2) down, turn the blower motor control to the Off position, wait until both LEDs illuminate (approximately 5 seconds) and then release the A/C mode switch.
4. When the A/C status indicator begins flashing DTCs, set the Mode switch to the floor position, simultaneously press the A/C mode switch and the EBL mode switch down until both LEDs start flashing (approximately 5 seconds) and then release the mode switches. Stored DTCs will clear from memory in approximately two seconds.