U1169 Loss of MMM Serial Data Communication - HVAC

CIRCUIT DESCRIPTION

DTC U1169 will set if the ignition is ON and the heater and A/C programmer has lost serial data communication with the Memory Mirror Module (MMM).

Diagnosis of this DTC is dependent upon other system symptoms (DTCs) being present with U1169.

TEST CONDITION(S)

1. Ignition in ON.

FAILURE CONDITION(S)

^ Open circuit.

ACTION TAKEN

1. Set DTC U1169.

TROUBLESHOOTING HINTS

1. Using a scan tool attempt to establish communications with MMM.
2. Check CKT 1807 for an open or short to power or ground.
3. Check that MMM is connected to power and ground.
4. If there are multiple Class 2 DTCs current check for a short to ground or voltage in CKT 1807. Refer to Computer System Diagnosis. Testing and Inspection