P0131 fault code: what it means

P0131: Bank 1 upstream O2 sensor voltage stays low (reads lean).

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

aged front O2 sensor
vacuum leak causing a real lean mixture
exhaust leak before the sensor
damaged sensor wiring

P0131 by make

Subaru

Front air-fuel ratio sensor signal is out of range (low). On Subaru this is the wide-band A/F sensor ahead of the cat.

Usual causes: failed front A/F sensor; A/F sensor wiring or connector fault; exhaust leak near the sensor

Suzuki

Front O2 sensor circuit low voltage.

Usual causes: failed front O2 sensor; exhaust leak before the sensor; wiring

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 P0131 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.