HVAC System

CIRCUIT DESCRIPTION
The calibrations for the heater and A/C control are stored in EEPROM. When the ignition is first turned On, the controller performs internal tests on the EEPROM and can determine the integrity of the EEPROM's non-volatile memory. The controller compares its previously stored checksum with the checksum calculated when the ignition was first turned On. If the two checksums do not match, the controller indicates that a calibration error (checksum error) has occurred.

CONDITIONS FOR SETTING THE DTC
^ The stored checksum does not match the calculated checksum.
^ The controller detects an internal memory malfunction (checksum error).
^ The condition is present when the ignition is first turned On.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 51 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 if the condition for the fault is no longer present.

TEST DESCRIPTION

Steps 1-2:

The number(s) below refer to the step number(s) on the diagnostic table.
2. Because the EEPROM is not removable from the heater and A/C control module and a DTC 51 is an internal malfunction to the controller, the repair procedure is to replace the heater and A/C control.