U1255 General Loss of Serial Data Communication - HVAC

CIRCUIT DESCRIPTION

This DTC refers to a generic loss of serial data communication with an unknown module. This code generally will set when the vehicle is first started, and the heater and A/C programmer or CCP requests information from another module and does not get a response. This DTC will clear when the module with the information that the heater and A/C programmer or CCP is requesting comes back on-line.

TEST CONDITION(S)

1. Ignition in ON.

FAILURE CONDITION(S)

1. Open circuit.

ACTION TAKEN

1. Set DTC U1255.

TROUBLESHOOTING HINTS

If DTC U1255 is set each ignition cycle even though the code was cleared, the following items should be checked.

1. Check DTCs for the IPC, Body Control Module (PZM) and PCM. If the IPC has set code DTC U1152 or if the PCM has set DTC P1605, replace the heater and A/C programmer. If the IPC, PCM or PZM has set code DTC U1153, replace the CCP.
2. Check the option bytes in the IPC. Make sure that the correct options have been programmed into the IPC. Refer to Computer System Diagnosis. Testing and Inspection
3. Check that the proper heater and A/C programmer has been installed in the vehicle.

If the three checks above are OK, the heater and A/C programmer and CCP is OK. Do not replace the components. Refer to Computer System Diagnosis. Testing and Inspection