Air Temperature Sensors

WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The vehicle uses the following air temperature sensors:

Outside
Inside
Upper right
Upper left
Lower right
Lower left

The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5 to +57.5°C (+20.3 to +135.5°F). When temperature increases the sensor signal decreases. The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module detects that one of the duct temperatures must change, the HVAC control module will adjust the appropriate air temperature actuator. The following list shows the duct sensors that are monitored by the HVAC control module in each mode position:

Mode Position	Duct Sensor Monitored
Vent	Upper left duct sensor and upper right duct sensor
Bi-Level	Upper left duct sensor and upper right duct sensor
Defog	Lower left duct sensor and lower right duct sensor
Floor	Lower left duct sensor and lower right duct sensor
Front Defrost	Lower left duct sensor and lower right duct sensor

If the HVAC control module detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored.

The inside temperature sensor operates within a temperature range between -6.5 to +57.5°C (+20.3 to +135.5°F). If the sensor is shorted to ground, an open, or shorted to voltage, the HVAC system will use a default value.

The outside temperature sensor operates within a temperature range between -30 to +51°C (-22 to +123.8°F). The OAT valve is received and displayed through the instrument panel cluster (IPC). If the IPC has determined that the outside temperature sensor has failed, the IPC shall display, 75, in place of the outside air temperature. If the sensor is shorted to ground, an open, or shorted voltage, the IPC will use a default value.

The IPC displays the outside air temperature value that it receives through a class 2 or GMLAN message. The scan tool has the ability to update the displayed ambient air temperature. The outside air temperature value is displayed or updated under the following conditions:

Condition	Display
At start up with the engine OFF more than 3 hours	Displays actual outside temperature
At start up with the engine OFF less than 3 hours	Displays last stored temperature
Vehicle moving above 16 km/h (10 mph) for 5 minutes	Updates temperature display at a slow filtered rate.
Vehicle moving at 51 km/h (32 mph) or greater for 2.5 minutes	Updates temperature display as rapidly as possible.
When the sensor reading is less than the displayed value.	Updates temperature display as rapidly as possible.
When the Front Defrost, Rear Defog and fan up buttons are pressed simultaneously.	Updates temperature display instantly.