What does B0338 mean on a Chevy?

B0338. Warmer control switch circuit malfunction. The HVAC module cannot read the warmer selection and the body warning light comes on. Applies to Chevrolet, GMC, Buick, Cadillac, Pontiac, Oldsmobile and Saturn models that use this code.

What causes B0338 on a Chevy?

Worn warmer position contacts in the HVAC control head Warmer switch signal circuit intermittent or shorted Corroded HVAC control head connector Failed HVAC control head Sticking warmer detent keeping the switch from closing

How do I fix B0338 on a Chevy?

Confirm the code with a scan tool Inspect and reseat the HVAC control head connector Backprobe the warmer switch signal circuit Monitor warmer switch status while turning the temperature knob Replace the HVAC control head only after circuit tests pass, then clear the code and retest

Code

B0338

Warmer control switch 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

B0338. Warmer control switch circuit malfunction. The HVAC module cannot read the warmer selection 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

Worn warmer position contacts in the HVAC control head
Warmer switch signal circuit intermittent or shorted
Corroded HVAC control head connector
Failed HVAC control head
Sticking warmer detent keeping the switch from closing

Standard procedure

Confirm the code with a scan tool
Inspect and reseat the HVAC control head connector
Backprobe the warmer switch signal circuit
Monitor warmer switch status while turning the temperature knob
Replace the HVAC control head only after circuit tests pass, 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: qualified. Read the source limits below.

Code B0338 definition | OBDII.pro
live manufacturer definition (obdii.pro)
Supports: GM manufacturer meaning for B0338
Fetched directly. The GM entry is the brand-family meaning used here. This site is independent of engine-codes and autocodes.
B0338 CHEVROLET Inside Air Temperature Sensor Open | Engine-Codes.com
archived reference page (engine-codes.com via Wayback Machine)
Supports: Chevrolet meaning and possible causes for B0338
Fetched directly. Model and year fitment remain curator claims.
B0338 CHEVROLET Inside Air Temperature Sensor Open | AutoCodes.com
archived reference page (autocodes.com via Wayback Machine)
Supports: corroboration of Chevrolet meaning and causes for B0338
Same Chevrolet text as the engine-codes page (both sites share one publisher).

Review note: obdii.pro GM names the climate control warmer switch circuit; the archived Chevrolet page names the inside air temperature sensor open. The circuits differ, so the record uses the GM wording and flags the conflict

Last updated 2026-10-10.

Report a correction for B0338. Include your vehicle, the issue and a source if you have one.