Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 182 (HVAC SYSTEM - AUTOMATIC)DIAGNOSTIC INFORMATION AND PROCEDURESAIR TEMPERATURE MALFUNCTIONCIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
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
- Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
- Ignition OFF, test for less than 10 ohms of resistance between the appropriate low reference circuit terminal and ground.
- Ambient air temperature sensor terminal B.
- Evaporator temperature sensor terminal 2.
- If greater than the specified range, test the low reference circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
- Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal B and the appropriate signal circuit terminal.
- Ambient air temperature sensor terminal A.
- Evaporator temperature sensor terminal 1.
- If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
- If all circuits test normal, test or replace the appropriate temperature sensor.
Sunload Sensor Circuit Malfunction
- Ignition OFF, disconnect the harness connector at the sunload sensor.
- Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal C and ground.
- If greater than the specified range, test the ground circuit for high resistance.
- Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal C and the appropriate signal circuit terminal.
- Left sunload sensor circuit terminal A.
- Right sunload sensor circuit terminal B.
- If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
- If all circuits test normal, test or replace the sunload sensor.
Inside Air Temperature Sensor Circuit Malfunction
- Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
- Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal 2 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.
- Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal 2 and the signal circuit terminal 1.
- If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
- If all circuits test normal, test or replace the inside air temperature sensor.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.