Heating Ventilation Air Conditioning (HVAC)

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

- Programming the heater and A/C control.
- The use of a scan tool.
- A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

Diagnostic Aids

- Install the scan tool
- Select PROGRAMMING from the HEATER and A/C CONTROL main menu.
- Program the heater and A/C control. Follow the instructions on the display screen.
- If the heater and A/C control can not be programmed with the scan tool, check all power and ground circuits to the controller. If OK, replace the controller.

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 if 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 Heater and A/C Control Replacement for the programming procedure.