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
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.
Reference Information
Schematic Reference
HVAC Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
* Air Temperature Description and Operation (Air Temperature Description and Operation)
* Air Delivery Description and Operation (Air Delivery 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
Ignition ON, observe 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.
Circuit/System Testing
Important: If any of the air temperature 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.
1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal 6 and ground.
• If greater than the specified range, test the low reference circuit for 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 ON, test for 4.8-5.2 volts between the low reference circuit terminal 6 and the signal circuit terminal 4.
• If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
5. If all circuits test normal, test or replace the inside air temperature sensor.
Component Testing
1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Install a 10-amp fused jumper wire between the ignition circuit terminal 1 and 12 volts. Install a jumper wire between the control circuit terminal 3 and ground. Verify the aspirator blower motor activates.
• If the aspirator blower motor does not activate, replace the inside air temperature sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Inside Air Temperature Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for HVAC control module replacement, setup, and programming