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.
Circuit/System Verification
2009 Chevrolet Tahoe Base, 4.8 CSECTION Circuit/System Verification
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, 2012 Chevrolet Suburban, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Check for bulletins before proceeding.
- Ignition ON, place the blower motor switch in each speed position. Verify that the blower motor operates properly in each position.
- If the blower motor does not operate properly in all speeds, refer to Blower Motor Malfunction .
- Using the scan tool observe the mode, temperature and recirculation door positions. Verify the actual and commanded door positions are within 4 counts of each other.
- If not within the specified range, refer to Circuit/System Testing DTC B0228, B0413, B0423, B0433, B3779, or B3782 .
- Engine ON, A/C ON, place the temperature control in the coldest position. Verify that the A/C compressor clutch engages.
- If the A/C compressor clutch does not engage, refer to Air Conditioning Compressor Malfunction .
- If the A/C compressor is engaged, but air is insufficiently cooled. Refer to Air Conditioning (A/C) System Performance Test (Long Wheel Base 1500) , Air Conditioning (A/C) System Performance Test (HP2) , Air Conditioning (A/C) System Performance Test (Short Wheel Base) , Air Conditioning (A/C) System Performance Test (Long Wheel Base 2500) .
- Turn the A/C OFF and place the temperature control in the warmest position.
- If the air is insufficiently heated refer to Heating Performance Diagnostic .
- Engine OFF, 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.
- 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.
- Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. Sensor parameter and Aux. 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.
- 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.
- Ignition ON, observe the scan tool A/C Evaporator Temperature Sensor parameter. The reading should be between -39°F (-35°C) and 208°F (98°C) and change with evaporator air temperature changes.
- If not within the specified range, refer to Evaporator Air Temperature Sensor Circuit Malfunction.
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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.