Heating-A/C System Diagnostics

HEATING-A/C SYSTEM DIAGNOSTICS

ON-BOARD DIAGNOSTICS

CAUTION: 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.

NOTE: Always inspect the IOD fuse prior to diagnosing any heating-A/C system concerns. Make sure the fuse is functional and fully seated into the terminals of the totally integrated power module (TIPM) located in the engine compartment.

The A/C-heater control communicates on the controller area network (CAN) B bus and is fully addressable with a scan tool.

The A/C-heater control's primary means of fault detection is through active and stored diagnostic trouble codes (DTCs). Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired in order to clear this type of DTC. Stored DTCs are those which occurred in the system since the A/C-heater control received the last clear diagnostic info message. All DTCs must be read with a scan tool.

The A/C-heater control's secondary means of fault detection is through system tests. These tests include the HVAC System Test, the A/C Cooldown Test, the Actuator Calibration Function, and for MTC Systems, the Actuator DTC Detection Test. Refer to System Tests for a detailed description of each test.

SYSTEM TESTS

HVAC System Test

The HVAC System Test, found in 24 - HVAC - Electrical Diagnostics, provides a starting point in the diagnostic process by identifying the appropriate system test to perform when diagnosing a given condition or DTC. It also provides a means for testing the entire HVAC system by utilizing the A/C-heater control's On-Board System Tests. The On-Board System Tests can also assist in diagnosing stored DTCs.

A/C Cooldown Test

The A/C Cooldown Test:

- is actuated with a scan tool.
- tests A/C system performance based on evaporator temperature sensor input.
- will fail if evaporator starting temperature is below 18° C (65° F) when initiating the test.
- will pass if the evaporator temperature drops 11° C (20° F).
- indicates test outcome by displaying one or more test status messages on the scan tool. These messages will clear after paging back out of this test function. Therefore, is it important to note all of the messages before doing so.
- will cause the A/C status indicator to flash while the test is running.

Actuator Calibration Function

The Actuator Calibration function:

- is actuated with a scan tool.
- homes and repositions door actuators.
- monitors for door span faults. Door span faults (XXX Door Travel Range Too Large or XXX Door Travel Range Too Small) will only display after calibration.
- will cause the electric backlight (EBL) status indicator to flash while the test is running.

Actuator DTC Detection Test

The Actuator DTC Detection Test:

- is actuated with a scan tool.
- supplements the continuous diagnostics on the actuator drive system.
- monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simultaneous shorts. Shorted actuator circuit faults (XXX Control Circuit High or XXX Control Circuit Low) will only display after running the Actuator DTC Detection Test.

After repairing each DTC, cycle the ignition switch, and then rerun the Actuator DTC Detection test to ensure that no new DTCs exist. If multiple DTCs are present, beginning with the common circuits, diagnose and repair all short high faults and then short low faults. When the test returns passed, proceed with troubleshooting by clearing faults and running the Actuator Calibration function as a final check of proper system operation.