Reading and Clearing Diagnostic Trouble Codes

The system functional test is used to detect system malfunctions that the self-test is unable to test. Refer to "FUNCTIONAL TEST" , and "DIAGNOSTIC SELF-TEST" if no error code is found to identify and repair system malfunctions.



1. Turn ignition off, then back on to reset the system.
2. Ensure engine coolant temperature is at least 120°F.
3. Set control head to Auto/90°F. Wait a minimum of 40 seconds, then verify the following conditions:
a. System goes to high blower and warm air is being discharged from floor.
b. Recirc door is in ``outside air'' position.
c. Warm air is bleeding out of defroster nozzle.
4. Enter ``self-test'', then record all faults and error codes displayed. Exit ``self-test'' and diagnose error code(s).
5. Set control head to Auto/60°F. Wait a minimum of 40 seconds, then verify the following conditions:
a. Cool air is being discharged from panel.
b. Recirc door is in ``recirc'' position.
6. Enter ``self-test'', then record all faults and error codes displayed. Exit ``self- test'' and diagnose error code(s).
7. Repeat steps 3 and 4.
8. Perform pinpoint tests H through P, if any other faults still exist. When diagnosing a vehicle at idle, the system will likely discharge cool air from the panel up to an ``85°'' set point due to engine heat acting on the ambient sensor. Because of this, the vehicle should be road tested as a final checkout.