Initial Inspection and Diagnostic Overview

SYSTEM DIAGNOSTICS
Fault detection is through active and stored Diagnostic Trouble Codes (DTCs)
- DTCs are displayed by the DRB III.
- 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 Module received the last "clear diagnostic info" message.

The A/C Cool-down Test:
- is actuated with the DRB III.
- checks A/C system performance based on evaporator temperature sensor input.
- will fail if evaporator temperature is below 18.3 °C (65 °F) when initiating the test.
- will pass if the evaporator temperature drops 6.7 °C (20 °F).
- faults display on the DRB III as test messages only after running the test.
- faults will not display on the DRB III as Diagnostic Trouble Codes.
- will cause the A/C mode switch status indicator to flash while the test is running.

If the test fails, the status indicator will continue to flash until either the test returns passed or the ignition key is cycled. It will also prevent the EBL mode switch status indicator (if equipped) from indicating EBL operating status. However the EBL mode switch will continue to function in this state.

The HVAC Door Recalibration function:
- is actuated with the DRB III.
After completing HVAC Door Recalibration, the DRB III will display the current total span of each door actuator. It is important to note this information before proceeding with diagnosing door calibration fault messages.

- homes and repositions door actuators.
- monitors for door span faults.
- faults display on the DRB III as test messages only after running the test.
- faults will not display on the DRB III as Diagnostic Trouble Codes.
- Will cause the EBL mode switch status indicator (if equipped) to flash while the test is running.
- If the test fails, the status indicator will continue to flash until either the test returns passed or the ignition key is cycled. It will also prevent the A/C mode switch status indicator (if equipped) from indicating A/C operating status. However, the A/C mode switch will continue to function in this state.

The Actuator Circuit Test:
- is actuated with the DRB III.
- monitors for shorted actuator circuits.
- allows service to easily diagnose and troubleshoot up to three simultaneous shorts.
- supplements the continuous diagnostics on the actuator drive system.
- faults display on the DRB III as test messages only after running the test.
- faults will not display on the DRB III as Diagnostic Trouble Codes when Performing The Actuator Circuit Test

CAUTION: To ensure a proper diagnosis, repair all Short Too Complex messages first, all common door driver circuit related messages second, and all other door driver circuit related messages last.

The DRB III can display up to three Actuator Circuit Test messages at a time. After repairing each Actuator Circuit Test message, cycle the ignition switch, then rerun the Actuator Circuit Test to ensure no new messages exist.

The Short Too Complex message:
- indicates that a specific determination of which lines are shorted could not be made.
- is caused by more than three drivers being shorted in the same direction. For example, four drivers all shorted to ground, or two or more drivers shorted with at least one driver shorted to ignition/battery and one driver shorted to ground.

Messages displaying:
- XXX Driver/Circuit Shorted to Ignition Battery will set on a per-driver basis.
- XXX Driver/Circuit Shorted to Ground will set on a per-driver basis.
- the same two drivers/circuits shorted to ignition/battery as-well-as shorted to ground indicates that two actuator driver circuits are shorted together.
- When the test returns passed, then troubleshooting should proceed to clearing faults and running the HVAC Door Recalibration system test as a final check of system health.