Without Scan Tool

The heater and the A/C programmer set the Diagnostic Trouble Codes (DTC) for the air conditioning system. One of the following methods may display the DTC:
^ The Scan Tool Display DTC selection
^ The on-board method
1. Press and hold the OFF, AUTO and the RECIRC buttons for 1 second.
2. The DTCs will display for 2 seconds each, and then return to normal operation.