P0131: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)

Common causes

• A failed upstream oxygen sensor
• A signal wire shorted to ground, or chafed wiring near the exhaust
• An exhaust leak near the sensor letting in outside air
• A real lean condition, such as a large vacuum leak

Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.

Symptoms

• Check engine light
• Poorer fuel economy
• Sometimes rough running or hesitation
• Possible failed emissions test

Is it safe to drive?

Usually drivable, but fix it soon; fuel control may be off, which wastes fuel and can harm the catalytic converter over time.

How to check it with a scanner

1. Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
2. Look for other codes such as P0171 (lean). If the engine is truly lean, fix that first.
3. On a warm engine, watch sensor 1 in live data. Many newer cars use a wideband (air-fuel ratio) sensor here that reads differently from older sensors, so compare against your vehicle's spec.
4. Inspect the wiring and connector, and check for exhaust leaks ahead of the sensor.
5. After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.

A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.

Questions

Related codes

• P0133: Upstream oxygen sensor slow, bank 1
• P0134: Upstream O2 sensor not responding, bank 1
• P0171: Engine running lean, bank 1
• P0132: Upstream O2 sensor voltage too high, bank 1
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• How to choose a car diagnostic scanner