For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Inside Air Temperature Sensor Signal | B0163 02 | B0163 05 | B0163 05 | 1
Ambient Air Temperature Sensor Signal | B0158 02 | B0158 05 | B0158 05 | 1
Upper Left Air Temperature Sensor Signal | B0173 02 | B0173 05 | B0173 05 | 1
Upper Right Air Temperature Sensor Signal | B0509 02 | B0509 05 | B0509 05 | 1
Lower Left Air Temperature Sensor Signal | B0178 02 | B0178 05 | B0178 05 | 1
Lower Right Air Temperature Sensor Signal | B0514 02 | B0514 05 | B0514 05 | 1
Low Reference | -- | B0173 05, B0158 05, B0163 05, B0509 05, B0178 05, B0514 05, B3933 05 | B0173 05, B0158 05, B0163 05, B0509 05, B0178 05, B0514 05, B3933 05 | 1
Right Sunload Sensor Signal | B0188 02 | B0188 05 | B0188 05 | 1
1. Air Temperature Malfunction

### Circuit/System Description

#### Air Temperature Sensors

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

• | Ambient Air Temperature Sensor

• | Inside Air Temperature Sensor Assembly

• | Upper Left Air Temperature Sensor

• | Upper Right Air Temperature Sensor

• | Lower Left Air Temperature Sensor

• | Lower Right Air Temperature Sensor

• | A/C Evaporator Temperature Sensor

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 +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts. The input of the duct air temperature sensors are different from the ambient and inside air temperature sensors. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the ambient and inside air temperature sensors will be displayed on the scan tool. The default value for the duct air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

#### Sun Load Sensor Assembly

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly. Low reference and signal circuits enable the sensor to operate. As the light shining upon the sensor gets brighter, the sensor resistance increases. The sensor signal decreases as the resistance increases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted sunload value. This value will not be displayed on the scan tool. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is fixed. The scan tool parameter for the sunload sensor is the actual state of the signal circuit.

### Diagnostic Aids

#### Ambient Air Temperature Display Update

Condition | Display
--- | ---
Using Scan Tool Special Function | Updates temperature display instantly
When the A/C and Recirc buttons are pressed simultaneously. | Updates temperature display instantly
At start up with the engine off less than 2 hours | Displays last stored temperature unless temperature has decreased. The outside air temperature reading is always instantly updated if ambient air temperature has decreased.
At start up with the engine off more than 2 hours | Displays actual outside temperature
Vehicle speed above 32 km/h (20 mph) for a minimum of 80 seconds | Updates temperature display at a filtered rate
Vehicle speed above 72 km/h (45 mph) | Displays actual outside temperature
Sensor ambient temperature reading is less than the last displayed value | Displays actual outside temperature
When the ambient air decreases | Updates temperature display rapidly

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Air Delivery Description and Operation

• | Air Temperature Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

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 Sun Load Sensor Circuit Malfunction.

2. Remove the shop towel and shine an incandescent light on the sunload sensor assembly. 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 Sun Load Sensor Circuit Malfunction.

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

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

4. 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 Ambient / Inside Air Temperature Sensor Circuit Malfunction.

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

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

6. Measure actual temperature using a thermometer at the A/C evap. temperature sensor. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter.

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

### Circuit/System Testing

#### Sun Load Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the Sunload Sensor.
2. Test for less than 10 ohms between the ground circuit terminal C and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the appropriate scan tool Sunload Sensor parameter is greater than 4.9 volts or 250 counts.

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

4. Install a 3-amp fused jumper wire between the appropriate signal circuit terminal A or B and the ground circuit terminal C. Verify the scan tool Sunload Sensor parameter is less than the 0.1 volt or 5 counts.

⇒ | If greater than 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.

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

#### Ambient / Inside Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate air temp sensor.
2. Ignition OFF, test for less than 10 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 Air Temp. Sensor Raw parameter is less than -35°C (-39°F).

⇒ | If greater 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 the low reference circuit terminal B. Verify the scan tool Air Temp. Sensor Raw parameter is greater than 85°C (185°F).

⇒ | If less 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 air temp sensor.

#### Duct Temperature / Evaporator Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate air temp sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 2 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 Air Temp. Sensor parameter is less than -35°C (-39°F).

⇒ | If greater 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.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Air Temp. Sensor parameter is greater than 85°C (185°F).

⇒ | If less 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 air temp sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Test for the appropriate resistance between the signal terminal A or 1 and the low reference terminal B or 2. Refer to Sensor Resistance Table for resistance values.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Duct Air Temperature Sensor Replacement - Upper Right Side

• | Duct Air Temperature Sensor Replacement - Upper Left Side

• | Duct Air Temperature Sensor Replacement - Lower Left Side

• | Duct Air Temperature Sensor Replacement - Lower Right Side

• | Ambient Air Temperature Sensor Replacement

• | Evaporator Air Temperature Sensor Replacement

• | Daytime Running Lamp (DRL) Ambient Light Sensor Replacement

• | Control Module References for HVAC control module replacement, programming and setup.