What does B0178 mean on a Chevy?

B0178. Lower output air temperature sensor circuit malfunction. The HVAC module cannot read the duct temperature and sets a body warning. Applies to Chevrolet, GMC, Buick, Cadillac, Pontiac, Oldsmobile and Saturn models that use this code.

What causes B0178 on a Chevy?

Failed lower output air temperature sensor with an out of range element Open or short in the lower output air temperature sensor signal circuit Corroded or loose lower output air temperature sensor connector Lower output air temperature sensor contaminated in the duct Faulty input inside the HVAC control module

How do I fix B0178 on a Chevy?

Confirm the code with a scan tool and compare the lower output air temperature reading to duct temperature Inspect and reseat the lower output air temperature sensor connector Test the lower output air temperature sensor and its signal circuit against the service chart Repair any chafed or open wiring before condemning the sensor Replace the lower output air temperature sensor only if its reading does not match duct temperature, then clear the code and retest

Code

B0178

Lower output air temperature sensor circuit malfunction

Category: Body
Severity: Body Warning Light
Applies to: Chevrolet, GMC, Buick, Cadillac, Pontiac, Oldsmobile and Saturn models that use this code
Related: No single generic twin. See OBD Codes List

What it means

B0178. Lower output air temperature sensor circuit malfunction. The HVAC module cannot read the duct temperature and sets a body warning. This Chevy-enhanced code applies to Chevrolet, GMC, Buick, Cadillac, Pontiac, Oldsmobile and Saturn models that use this code.

Findings, check these first

Failed lower output air temperature sensor with an out of range element
Open or short in the lower output air temperature sensor signal circuit
Corroded or loose lower output air temperature sensor connector
Lower output air temperature sensor contaminated in the duct
Faulty input inside the HVAC control module

Standard procedure

Confirm the code with a scan tool and compare the lower output air temperature reading to duct temperature
Inspect and reseat the lower output air temperature sensor connector
Test the lower output air temperature sensor and its signal circuit against the service chart
Repair any chafed or open wiring before condemning the sensor
Replace the lower output air temperature sensor only if its reading does not match duct temperature, then clear the code and retest

Look up another code

Press / to jump to the box. Chevy-enhanced powertrain, body, chassis and network codes.

Sources and review

Review: checked against the recorded source material.

Code B0178 definition | OBDII.pro
live manufacturer definition (obdii.pro)
Supports: GM manufacturer meaning for B0178
Fetched directly. The GM entry is the brand-family meaning used here. This site is independent of engine-codes and autocodes.
B0178 CHEVROLET Output Air Temperature Sensor 2 Circuit | Engine-Codes.com
archived reference page (engine-codes.com via Wayback Machine)
Supports: Chevrolet meaning and possible causes
Fetched directly. Model and year fitment remain curator claims.
B0178 CHEVROLET Output Air Temperature Sensor 2 Circuit | AutoCodes.com
archived reference page (autocodes.com via Wayback Machine)
Supports: corroboration of Chevrolet meaning and causes
Same Chevrolet text as the engine-codes page (both sites share one publisher).

Last updated 2026-10-10.

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