Volt

DTC B0173, B0178, or B3933

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

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +85°C (-40 to +185°F). The sensor signal varies between 0-5 V. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module detects a malfunctioning sensor, then the control module software will use a default air temperature value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

The vehicle is turned ON.

The HVAC control module detects the sensor signal out of range. The signal voltage is less than 0.1 V or greater than 4.9 V for more than 50 ms.

A default value is used when the DTC is set.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Vehicle OFF and all vehicle systems OFF, disconnect the harness connector at the appropriate temperature sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 Ω between the low reference circuit terminal B and ground.

⇒	If 10 Ω or greater

2.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

2.2.	Test for less than 2 Ω in the low reference circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, replace the K33 HVAC control module.

⇓	If less than 10 Ω

3. Vehicle in Service Mode.
4. Verify the scan tool parameter is less than -39°F.

•	Lower Left Duct Air Temperature Sensor

•	Upper Left Duct Temperature Sensor

•	A/C Evaporator Temperature Sensor

⇒	If greater than -39°F

4.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

4.2.	Test for infinite resistance between the signal circuit terminal A and ground.

⇒	If less than infinite resistance, repair the short to ground on the circuit.

⇒	If infinite resistance, replace the K33 HVAC control module.

⇓	If -39°F or less

5. Install a 3 A fused jumper wire between the signal circuit and the low reference circuit terminal B.
6. Verify the scan tool parameter is greater than 240°F.

•	Lower Left Duct Air Temperature Sensor

•	Upper Left Duct Temperature Sensor

•	A/C Evaporator Temperature Sensor

⇒	If 240°F or less

6.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, vehicle in Service Mode.

6.2.	Test for less than 1 V between the signal circuit and ground.

⇒	If 1 V or greater, repair the short to voltage on the circuit.

⇓	If less than 1 V

6.3.	Vehicle OFF

6.4.	Test for less than 2 Ω in the signal circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, replace the K33 HVAC control module.

⇓	If greater than 240°F

7. Test or replace the temperature sensor.

1. Test the air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
2. Compare the readings with the Sensor Resistance Table and verify that the resistance is within 5 percent of the specification.

⇒	If not within the specified range, replace the sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.