Auxiliary air temperature actuator circuit fault
What it means
B0428. Auxiliary air temperature actuator circuit fault. The rear air mix door cannot reach the commanded position and the body warning light comes on.. This Chevy-enhanced code applies to Chevrolet, GMC, Buick, Cadillac, Pontiac, Oldsmobile and Saturn models that use this code.
Findings, check these first
- Failed rear auxiliary air temperature actuator
- Open or short in the rear auxiliary actuator control circuit
- Corroded rear auxiliary actuator connector
- Rear air mix door binding in its travel
- Faulty output in the auxiliary HVAC control module
Standard procedure
- Confirm the code with a scan tool
- Inspect and reseat the rear auxiliary actuator connector
- Test the rear auxiliary actuator control circuit for opens and shorts
- Command the rear air mix door with the scan tool and watch its travel
- Replace the rear auxiliary actuator or auxiliary HVAC control module only after circuit tests pass, then clear the code and retest
Look up another code
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Sources and review
Review: qualified. Read the source limits below.
- B0428 CHEVROLET Code: Meaning, Causes, and Symptoms | OBD2 Codes - OBD2 Codes
live reference page (obd2-codes.co)
Supports: CHEVROLET and GM-family meaning and likely causes for B0428
Fetched directly. B0428 reads "Auxiliary Air Temperature Actuator".
- Code B0428 meaning and causes | OBDII.pro
live reference page (obdii.pro)
Supports: independent corroboration of the GM meaning
Fetched directly. obdii.pro is a separate publisher and gives the GM meaning as: Air Mix Door #3 Inoperative Error More details about the error B0428 and possible reasons for its occurrence.
Source caveat: obdii.pro GM meaning: "Air Mix Door #3 Inoperative Error More details about the error B0428 and possible reasons for its occurrence"
Last updated 2026-10-10.
Report a correction for B0428. Include your vehicle, the issue and a source if you have one.