Forced Calibration: The ATC module can be manually forced to carry out a calibration routine on the stepper motors. This can be carried out by holding down the ECON and recirculation buttons on the ATC module panel while simultaneously switching the ignition on. The ATC module will now carry out a calibration routine on the stepper motors, but will flash the ECON LED rather than the programmed de-frost LED.

Distribution motor self-test The motor and flap operation can be checked using the on-board distribution motor self-test function. The self-test can be initiated by pressing and holding the ECON and RECIRC buttons while turning the ignition switch to the ON position. The control module will then compare the current motor position with the values stored in the module and will indicate an error by flashing the ECON LED (light emitting diode). If there are no errors, the LED will go out and the system will function normally. To confirm that there are no errors, turn the ignition switch to the OFF position, then back to the ON position. Observe the operation of the programmed defrost LED. If there are errors present, the programmed defrost LED will flash and the system will attempt to calibrate itself. For additional information on the function of the system, refer to the relevant section of the workshop manual.

Stepper Motor Diagnostics
Fault diagnosis on the heater stepper motors falls into two main groups:
- Electrical fault: A diagnostic trouble code (DTC) will be raised and logged in the ATC module memory.
- Mechanical fault: The programmed de-frost LED will blink to indicate the ATC module is attempting to carry out a calibration routine.

A calibration routine will be initiated by the ATC module if any of the following occur:
- One or more of the stepper motors is replaced.
- The ATC module is replaced.
- A foreign object enters the system and causes a stepper motor to stall.
Stepper motor related DTCs are stored in the ATC module memory and can be retrieved using T4. For additional information, refer to: Climate Control System Diagnosis and Testing).