U1255 Generic Loss of Communication - HVAC

Circuit Description

The HVAC programmer periodically sends a request for information to other modules on the Class 2 data line.

Diagnosis of this DTC is dependent upon other system symptoms (DTC) present with U1255.

DTC Will Set When

The HVAC programmer requests information and the module which has the information is not "On-Line."

Action Taken

The HVAC programmer will use default values from the information that is was requesting.

DTC Will Clear When

The module with the information the HVAC programmer is requesting comes back "On-Line."

Troubleshooting Hints

If DTC U1255 is set, clear DTCs and cycle ignition. If DTC U1255 is still current, ensure that all the modules are functioning properly and the Class 2 data bus is not shorted to ground or to voltage. If the Class 2 data bus and all of the modules on it are working properly, replace the HVAC programmer.