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-volitale
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 occured.
Conditions for Setting the DTC
| • | The stored checksum does not match the calculated checksum. |
| • | The controller detects an internal memory malfunction (checksum
error). |
| • | This condition must occur 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. |
Diagnostic Aids
Because the EEPROM is not removable from the heater and A/C control
and a DTC 51 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.
