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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/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 air temperature sensor
* Lower 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. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease.

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.

Heater Core Coolant Pump

The primary purpose of the heater core coolant pump is to circulate engine coolant through the HVAC heater core when heat is required in the cabin for comfort. This normally happens when the vehicle is in an Auto Stop and the mechanical pump is not spinning. If the HVAC control module has determined heat is needed for the cabin, this pump is turned on once the engine is shut off so the customer does not notice a change in heater duct discharge temperatures. The SGCM starter generator control module controls the auxiliary coolant pump. Heater core coolant pump relay supplies voltage to the heater core coolant pump.

Diagnostic Aids





Reference Information
Schematic Reference

HVAC Schematics (HVAC - Automatic)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Air Delivery Description and Operation (Air Delivery Description and Operation)
* Air Temperature Description and Operation (Air Temperature Description and Operation)

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 Sun Load Sensor Circuit Malfunction.

2. 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 Air Temperature Sensor Circuit Malfunction.

3. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. Sensor 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 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 Sensor Circuit Malfunction.

5. Ignition ON, command the heater core pump ON and OFF with a scan tool. Observe the operation of heater core pump.

• If the heater core coolant pump does not turn on and off with each command , refer to Heater Core Coolant Pump 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, test for 4.8-5.2 volts between the ground circuit terminal C and the appropriate signal circuit terminal listed below:

* Left solar load sensor circuit terminal A
* Right solar load sensor circuit terminal B

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

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

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 ohms between the following 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 Outside Air Temp. Raw parameter is less than -35°C (-39°F).

• If greater than the specified range, test the following 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 following signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Outside Air Temp. 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 ambient air temperature sensor.

Inside Air Temperature Sensor Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Test for less than 1 ohm 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 a test lamp illuminates between the control circuit terminal B and ground.

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

4. 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 an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. Ignition ON, verify that the scan tool Inside Air Temp. Sensor 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.

6. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal D. Verify the scan tool Inside Air Temp. Sensor is greater than 98°C (208°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.

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 duct temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 2 listed below 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 that the appropriate scan tool Duct Actual 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 1 and the low reference circuit terminal 2. Verify the appropriate scan tool Duct Actual parameter is greater than 98°C (208°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 appropriate duct temperature sensor.

Heater Core Coolant Pump Malfunction
1. Ignition OFF, disconnect the harness connector at the heater core coolant pump.
2. Ignition ON, verify that a test lamp illuminates between the control circuit terminal B and ground while commanding the pump ON and OFF with a scan tool.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the SGCM.

3. Verify that a test lamp illuminates between the B+ circuit terminal A and ground.

• If the test lamp does not light, test the B+ circuit for a short to ground, open or high resistance. If the circuit tests normal, replace the Coolant heater pump

Component Testing

1. A thermometer can be used to test the sensor off the vehicle in warn and or cold water. Sensor Resistance Table (HVAC - Automatic) for this test.
2. Test the appropriate temperature sensor by varying the sensor temperature in water while monitoring the sensor resistance.
3. Compare the readings with the Temperature vs Resistance table and verify that the resistance is within 5 percent of the specification.

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

Repair Instructions

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

* Duct Air Temperature Sensor Replacement - Upper (Duct Air Temperature Sensor Replacement - Upper)
* Duct Air Temperature Sensor Replacement - Lower (Duct Air Temperature Sensor Replacement - Lower)
* Inside Air Temperature Sensor Replacement (Service and Repair)
* Headlamp Automatic Control Ambient Light Sensor Replacement (Service and Repair)
* Heater Coolant Pump Replacement (HP5) ()Heater Coolant Pump Replacement (LAT) ()
* Control Module References (Programming and Relearning) for HVAC replacement, setup, and programming

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