HVAC System - Automatic

CIRCUIT DESCRIPTION
DTC 55 is an internal control unit hardware failure (RAM, ROM defective) in the heater and A/C control.

CONDITIONS FOR SETTING THE DTC
^ The heater and A/C control detects an internal hardware malfunction.
^ The heater and A/C control checks the hardware on a continuous basis every 200 ms.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 55 in the controllers memory.
^ Disables all heater and A/C control functions.

CONDITIONS FOR CLEARING THE DTC
^ The condition for the fault is no longer present.
^ The use of a scan tool.
^ A history DTC will clear after 20 consecutive ignition cycles it the condition for the fault is no longer present.

DIAGNOSTIC AIDS
Because a DTC 55 is an internal malfunction to the controller, the repair procedure is to replace the heater and A/C control. Program the new heater and A/C control. Refer to Control Assembly Replacement for the programming procedure.