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Tech Tip: GM Truck HVAC Out of Control

May 13, 2008

By Rich Diegle
ALLDATA Senior Automotive Editor

Some GM truck and SUV owners may comment that they cannot control the heating, ventilation and air conditioning (HVAC) system. Others may comment that the HVAC system defaults to the Defrost mode.

If a technician checks for diagnostic trouble codes (DTC), they could find that the following DTCs have set:
B0229 - Recirculation Actuator
B0414 - Left Air Temperature Actuator
B0424 - Right Air Temperature Actuator
B3770 - Mode Actuator Cause

The problem may be that the HVAC actuator harness has contacted a sharp edge on the instrument panel support brace, causing a rub through condition and a grounding of the actuator control and/or feedback circuits.

Models affected: 2003-’05 Cadillac Escalade, Escalade ESV, Escalade EXT; Chevrolet Avalanche, Silverado (pictured), Suburban, Tahoe; and GMC Sierra, Yukon, Yukon XL

1. To repair the problem, locate the HVAC actuator harness contact point shown by the arrow in Figure 1.

Note: The illustration is of the instrument panel with the instrument panel compartment door opened and folded downward. The actuator harness is located in the left side of the opening in the instrument panel.

2. Inspect the HVAC actuator harness for contact with the instrument panel support brace. Repair any damage to the actuator harness wiring.

3. Install a protective plastic conduit over the harness.

4. Install friction tape over the sharp edge of the instrument panel brace to insulate it.

5. Clear the diagnostic trouble codes and verify proper HVAC system operation.

ALLDATA Senior Automotive Editor Rich Diegle is an Advanced Engine Performance Certified, ASE Master Technician with an AA Degree in automotive technology and 23 years of dealership and independent shop experience.

Courtesy of ALLDATA.

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