P0031: HO2S Heater Control Circuit Low (Bank 1 Sensor 1)

What does P0031 mean?

The heater-control measurement for the bank 1 upstream exhaust sensor is below its calibrated limit. The upstream sensor needs heat for early mixture control, but this is a heater electrical diagnosis, not the low oxygen-signal fault P0131. The exact low-side/high-side test depends on the vehicle circuit.

Generic OBD-II definition: HO2S Heater Control Circuit Low (Bank 1 Sensor 1). Confirm applicability in your vehicle service information.

Common causes

• Heater-control wiring shorted to ground
• Failed heater element
• Damaged upstream connector

Symptoms

• Check engine light
• Slow entry into closed-loop fuel control
• Possible decrease in fuel economy

Diagnostic focus

This low-control result concerns the upstream heater, not a lean exhaust reading. P0131 is the separate bank 1 upstream low-signal code.

Can I keep driving with P0031?

Severity: Medium If the engine runs normally and the light is steady, arrange emissions-system diagnosis. Stop for a flashing light or severe roughness; those symptoms need separate urgent attention.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Allow the exhaust to cool before inspecting wiring
• Check for a ground short and verify the heater supply under the manufacturer test conditions.
• Repair wiring or replace the correct sensor only when the fault is confirmed

Sources & review

• OBD-Codes.com: P0031
• TroubleCodes.net: generic code definitions

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.