HVAC Systems - Automatic Diagnosis

Schematic:

CIRCUIT DESCRIPTION
The Instrument Panel Module (IPM) communicates with the heater and A/C control via the Keyboard Display Driver (KDD) data bus. This communication link is only used by the IPM and the heater and A/C control.

CONDITIONS FOR RUNNING THE DTC
The ignition is turned ON.

CONDITIONS FOR SETTING THE DTC
^ There is a loss of communications between the IPM and the heater and A/C control.
^ The above conditions are present for 3 seconds

ACTION TAKEN WHEN THE DTC SETS
The heater and A/C system will be disabled.

CONDITIONS FOR CLEARING THE DTC
^ The DTC will become history if the IPM 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.

TEST DESCRIPTION

Steps 1-10:

Steps 11-19:

The number(s) below refer to the step number(s) on the diagnostic table.
4. This step verifies that the heater and A/C control is functioning, but not communicating with the IPM