P0031 fault code: what it means

P0031: Bank 1 upstream oxygen / air-fuel sensor heater circuit reads low, usually a burnt-out heater inside the sensor.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

failed heater inside the front O2 / A/F sensor
blown O2 sensor heater fuse
broken or corroded sensor wiring

P0031 by make

Nissan

Front air-fuel ratio sensor heater (bank 1) circuit low, so the sensor is slow to work.

Usual causes: failed front A/F sensor (heater); blown fuse or relay in heater circuit; wiring or connector fault

Subaru

Front air-fuel ratio sensor heater circuit reads low. The heater lets the sensor work from cold; fuel control suffers until it warms.

Usual causes: failed front A/F sensor heater (replace sensor); blown heater fuse or wiring fault; corroded sensor connector

What the repair usually costs

Air-fuel ratio / front O2 sensor replace (upstream)NZ$270–NZ$750 · A$260–A$730
O2 sensor replace (downstream / after cat)NZ$180–NZ$480 · A$180–A$460

Not sure what P0031 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.