Introduction

The Automatic Temperature Control (ATC) control module has a system self-diagnostic mode. The ATC control module is capable of troubleshooting each of its input and output circuits. When the control module detects a fault and places it in memory, an "Er" is momentarily displayed in the heater-A/C control panel vacuum fluorescent display area, but it will only be displayed once during each ignition cycle. The ATC system can also be diagnosed using a DRB scan tool and the proper Diagnostic Procedures.

The ATC control module is capable of three different types of self-diagnostic tests, as follows:

- Fault Code Tests
- Input Circuit Tests
- Output Circuit/Actuator Tests