B0180

CIRCUIT DESCRIPTION
The HVAC control module monitors the lower duct air temperature via a lower air temperature sensor. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low. The HVAC control module requests the A/C compressor clutch engagement and controls the air temperature actuator door position in order to maintain the temperature selected on the HVAC control module.

CONDITIONS FOR RUNNING THE DTC
The ignition is turned ON.

CONDITIONS FOR SETTING THE DTC
The HVAC control module detects the fault when the signal circuit is less than 0.09 volts.

ACTION TAKEN WHEN THE DTC SETS
The HVAC control module uses a default temperature sensor value until the fault is cleared.

CONDITIONS FOR CLEARING THE DTC
^ The DTC becomes history when the HVAC control module no longer detects a failure.
^ The history DTC clears after 50 fault free ignition cycles.
^ The DTC can be cleared with a scan tool.

DIAGNOSTIC AIDS
^ Visually inspect the sensor connector and harness for corrosion and damage. The resistance value of the sensor must be between 47-101,000 Ohm. If the resistance is not within the specified value, replace the sensor.
^ Insure lower air temperature sensor is in place and secure. Insure no restrictions or debris around lower air temperature sensor this will give incorrect reading to HVAC control module.
^ If condition is not present, refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-4:

Steps 5-12:

The numbers below refer to the step numbers on the diagnostic table.
2. Scan tool uses a default value, this will not give accurate reading of sensor value if open or short to ground.
8. Tests for the possibility of a short to another 5 V reference circuit.