HVAC Systems - Automatic Diagnosis

Schematic Reference HVAC Air Delivery/Temperature Control Schematics

Steps 1-3:

CIRCUIT DESCRIPTION
The HVAC (ECC) module communicates with the Body Control Module (BCM) via the data bus. This communication link is used by all modules on the Class II data link.

CONDITIONS FOR RUNNING THE DTC
The ignition is turned ON.

CONDITIONS FOR SETTING THE DTC
- There is a checksum (EEPROM) and (ROM) error within the HVAC (ECC) controller.
- The above conditions are present for 30 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The automatic portion of the heater and A/C system will be disabled.
- Upon any ignition signal to the HVAC (ECC) module, the ECC shall compute a checksum value for EEPROM and a check sum value for ROM and compare them to their respective checksum reference values stored in the ECC controller. If either calculated checksum value is not equal to its respective checksum reference value, the DTC shall set to a current code.

CONDITIONS FOR CLEARING THE DTC
- The DTC will become history if the HVAC Module no longer detects a failure.
- The history DTC will clear after 50 fault free ignition cycles.
- The DTC can be cleared with a scan tool.