O2 sensor low voltage (B1S1)
What P0131 means
Your car's computer set P0131: O2 sensor low voltage (B1S1). It belongs to the fuel and air metering group of codes. It is a generic code, so it means the same thing on every make. The check engine light usually comes on once the fault has been seen on two drives in a row. Until then it shows up as a pending code.
Can I keep driving? Usually safe to drive for now, but get it checked soon. Left alone it can lower fuel economy, fail an emissions test or lead to a bigger repair.
Common causes
- Ageing or contaminated oxygen sensor
- Exhaust leak in front of the sensor
- Wiring or connector damage
- A real fuel mixture problem the sensor is reporting
Fix the cheapest, most likely cause first. Clearing the code without a repair only turns the light off until the fault comes back.
Check it yourself
Graph the O2 sensor voltage and short-term fuel trim. A healthy upstream sensor switches quickly between about 0.1 and 0.9 V.
Torque Deck reads P0131 with a cheap Bluetooth OBD2 adapter. It also shows the freeze frame (engine conditions at the moment the code set) and the live data you need to narrow it down.
Parts
Parts most often replaced for P0131: upstream oxygen sensor. Confirm the cause first, and match the part to your exact engine.
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Related codes
This page explains what the code usually means. It is not a diagnosis of your car. When in doubt, ask a mechanic.