The HVAC control module supplies inside and ambient air temperature sensors with a low reference circuit and 5-volt signal circuit. The inside air temperature sensor has a fan motor that operates using body ground and a 12-volt supply from the body control module (BCM) when the ignition and HVAC control module are ON. The HVAC control module determines the voltage drop across the sensors, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

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. Ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. Verify the scan tool Right Sunload Sensor and Left Sunload Sensor parameters are within 3 counts of each other.

⇒	If not within the specified range, refer to Sunload Sensor Circuit Malfunction.

2. Measure actual outside air temperature using a thermometer. Compare this value to the scan tool Ambient Air Temp. Sensor parameter. The measured temperature should be within 5 degrees of parameter.

⇒	If not within the specified range, refer to Ambient Air Temperature Sensor Circuit Malfunction.

3. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of parameter.

⇒	If not within the specified range, refer to Inside Air Temperature Sensor Circuit Malfunction.

4. Measure actual air temperature using a thermometer at each duct temperature sensor. Compare this value to the appropriate scan tool Duct Temp. Sensor parameter. The measured temperature should be within 5 degrees of parameter.

⇒	If not within the specified range, refer to Duct Temperature Sensor Circuit Malfunction.

Sunload Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the sunload sensor assembly.
2. Test for less than 2.0 ohm between the low reference circuit terminal C and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal replace the HVAC control module.

3. Ignition ON, verify the Left Sunload Sensor parameter is greater than 250 counts.

⇒	If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Ignition ON, verify the Right Sunload Sensor parameter is greater than 250 counts.

⇒	If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the HVAC control module.

5. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal C. Verify the Left Sunload Sensor parameter is less than 5 counts.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

6. Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal C. Verify the Right Sunload Sensor parameter is less than 5 counts.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

7. If all circuits test normal, test or replace the sunload sensor assembly.

Ambient Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the ambient air temperature sensor.
2. Ignition OFF, test for less than 10.0 ohms between the low reference circuit terminal B and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal replace the HVAC control module.

3. Ignition ON, verify the scan tool Ambient Air Temp. Sensor parameter is greater than 250 counts.

⇒	If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the appropriate Ambient Air Temp. Sensor parameter is less than 5 counts.

⇒	If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. If all circuits test normal, test or replace the ambient air temperature sensor.

Inside Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal 1 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for short to ground or an open/high resistance.

3. Ignition ON, HVAC control module ON. Verify that a test lamp illuminates between the ignition circuit terminal 1 and the control circuit terminal 3.

⇒	If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

4. Ignition OFF, test for less than 10.0 ohms between the low reference circuit terminal 3 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal replace the HVAC control module.

5. Ignition ON, verify the scan tool Inside Air Temp. Sensor parameter is greater than 250 counts.

⇒	If less than the specified range, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the HVAC control module.

6. Install a 3A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Inside Air Temp. Sensor parameter is less than 5 counts.

⇒	If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

7. If all circuits test normal, test or replace the inside air temperature sensor.

Duct Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 10.0 ohms between the low reference circuit terminal B and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal replace the HVAC control module.

3. Ignition ON, verify the appropriate scan tool Temp. Sensor parameter is greater than 250 counts.

⇒	If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the appropriate scan tool Temp. Sensor parameter is less than 5 counts.

⇒	If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. If all circuits test normal, test or replace the temperature sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.