Faulty O2 sensor. Exhaust leak before sensor. Vacuum leak causing lean condition. Wiring short to ground. Contaminated sensor (coolant or oil).

Which cars are affected by P0131?

P0131 is most commonly reported on Ford, Vauxhall, Toyota, Nissan, Hyundai vehicles, but can appear on any make.

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P0131

Medium severity

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

The upstream oxygen sensor on bank 1 is reporting a consistently low voltage, indicating a lean exhaust condition or a sensor fault. The ECM uses this sensor for fuel trim adjustments.

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Common causes of P0131

1Faulty O2 sensor

2Exhaust leak before sensor

3Vacuum leak causing lean condition

+2 more causes

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Commonly affected vehicles

FordVauxhallToyotaNissanHyundai

P0131 can appear on any vehicle — these are the makes where it is most frequently reported.

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Related fault codes

P0171Medium

System Too Lean (Bank 1)

P0300High

Random/Multiple Cylinder Misfire Detected

P0420Medium

Catalyst System Efficiency Below Threshold (Bank 1)

P0172Medium

System Too Rich (Bank 1)