Central Control Module (CCM)

Circuit Description

The rear defogger relay coil circuit is completed by the CCM (if the engine is running) when it receives a "defogger on" request from the rear defog switch; the CCM grounds CKT 291, energizing the relay coil.

Code 22 will set when CKT 291 is in a high state (not grounded by the CCM) for more than 600 milliseconds while the CCM is attempting to actuate the rear defogger relay.

Test Description

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks for a short to B+ in CKT 291.
2. This test checks for an internal short in the relay between terminals "4" and "2", which would cause a short to battery condition by allowing power from the Defogger circuit breaker into the circuit.
3. This checks for an internal open in the relay.
4. This test checks for proper CCM control of the circuit by telling the CCM to cycle the ground at terminal "2" "ON" and "OFF." If the connection at the CCM, the wiring, and the relay connector are good but the test light does not cycle "ON" and "OFF," the CCM is faulty and should be replaced.

Diagnostic Aids

If the code is a history code, the problem may be intermittent. Try performing the tests shown while "wiggling" wiring and connectors; this can often cause the fault to appear. Check for poor connections at both the CCM and the rear defogger relay connector; these could cause an open or an intermittent fault. Refer to "Intermittents/Poor Connections".

If CKT 291 is shorted to battery, the vehicle may exhibit a no-crank condition. Also, if equipped with C68 Electronic Climate Control, the HVAC blower fan may run, even with the HVAC system and the ignition "OFF."