Can a vacuum leak cause P0131?

Yes — a vacuum leak causes a real lean condition that makes the O2 sensor read low voltage. Fix vacuum leaks before replacing the sensor.

How do I tell if it is the sensor or a leak?

If fuel trims are high positive and the engine runs rough, look for vacuum leaks first. If trims are normal but O2 is stuck low, the sensor is bad.

Medium Severity

Emissions System

The upstream O2 sensor on bank 1 is stuck at a low voltage, indicating a lean exhaust condition. Could be the sensor or an actual lean condition.

Common Fix

Replace upstream O2 sensor

Estimated Cost (DIY)

$30 - $100

Failed O2 sensorlikely

Vacuum leak causing actual lean conditionpossible

Exhaust leak before sensorpossible

Low fuel pressurepossible

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Can a vacuum leak cause P0131?: Yes — a vacuum leak causes a real lean condition that makes the O2 sensor read low voltage. Fix vacuum leaks before replacing the sensor.
How do I tell if it is the sensor or a leak?: If fuel trims are high positive and the engine runs rough, look for vacuum leaks first. If trims are normal but O2 is stuck low, the sensor is bad.

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