P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)

What it means

The signal voltage of the upstream oxygen sensor on bank 1 stayed below the calibrated threshold, typically under about 0.1 V, for longer than the monitor allows. A permanently low voltage means the sensor reports a constant lean condition, either because the mixture really is lean or because the circuit is shorted to ground. The ECM responds with large positive fuel trims, which causes rough idle, hesitation, higher consumption and a lit MIL.

Likely causes (most common first)

1. Genuinely lean mixture from an intake or exhaust leak
2. Sensor signal wire shorted to ground
3. Low fuel pressure, clogged filter or restricted injectors
4. Aged sensor stuck at low output
5. Open circuit in the sensor signal or ground line
6. Faulty engine control module input

Can you drive with it?

Short journeys are acceptable, but a persistently lean mixture can overheat the catalyst and should be diagnosed soon.