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Air Temperature Malfunction




Air Temperature Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit Description

Evaporator, Inside and Ambient Air Temperature Sensors

The HVAC control module supplies the evaporator, 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 HVAC control module 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.

Sunload Sensor Assembly

The sunload sensor is a 2-wire photo diode. Body ground and 5-volt signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and very bright. The sunload sensor provides the HVAC control module with a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Reference Information
Schematic Reference

HVAC Schematics (HVAC - Automatic)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Automatic HVAC Description and Operation (HVAC - Automatic)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)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 Sunload Sensor Circuit Malfunction.

2. Remove the shop towel and shine a flashlight 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 Sunload 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 Evaporator and Ambient 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 Inside Air Temperature Sensor Circuit Malfunction.

5. Measure actual evaporator air temperature using a thermometer. 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 Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.

Circuit/System Testing

Important: If any of the air temperature sensors or sunload sensors have an out of range condition caused by a short to voltage, short to ground, or an open/high resistance a diagnostic trouble code (DTC) will set. The following tests describe conditions that can cause inaccurate information to be processed in the HVAC control module and also operate between the minimum and maximum operating range without setting a DTC.

Evaporator and Ambient Air Temperature Sensor Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the appropriate temperature 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 high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal B and the signal circuit terminal A.

• If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.

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

Sunload Sensor Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the sunload sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal C and ground.

• If greater than the specified range, test the ground circuit for high resistance.

3. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal C and the appropriate signal circuit terminal listed below.

* Left sunload sensor circuit terminal A.
* Right sunload sensor circuit terminal B.

• If less than the specified range, test the signal circuit for a high resistance. If the circuit tests normal, replace the HVAC control module.

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

Inside Air Temperature Sensor Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Ignition OFF, 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 high resistance.

3. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal D and ground.

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

4. Ignition ON, HVAC control module ON. Verify that a test lamp illuminates between the ground circuit terminal C and the control circuit terminal B.

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

5. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal D and the signal circuit terminal A.

• If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.

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

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Ambient Air Temperature Sensor Replacement (Service and Repair)
* Sun Load Temperature Sensor Replacement (Service and Repair)
* Inside Air Temperature Sensor Replacement (Service and Repair)
* Heater and Air Conditioning Control Wiring Harness Replacement (w/Evaporator Temperature Sensor) (HVAC - Automatic)
* Control Module References (Programming and Relearning)for HVAC control module replacement, setup, and programming

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