P0131
Medium SeverityO2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
Emissions System
P0131 — Instant Answer
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
Severity: MEDIUM SEVERITY
Meaning: 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.
Safe to drive? Usually yes with caution, but confirm root cause before long trips.
Estimated repair cost: $30 - $100
Most common causes:
- 1. Failed O2 sensor (35-45% of cases)
- 2. Vacuum leak causing actual lean condition (10-25% of cases)
- 3. Exhaust leak before sensor (10-25% of cases)
- 4. Low fuel pressure (10-25% of cases)
Symptoms
- ⚠️Poor fuel economy
- ⚠️Rough idle
- ⚠️Hesitation
- ⚠️Check engine light
Related Symptoms
Common Causes
How to Diagnose P0131
- 1Check for vacuum leaks
- 2Check fuel pressure
- 3Monitor O2 sensor voltage
- 4If sensor stuck below 0.3V, replace it
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0131.
Related Symptoms
Browse →Rough idle often traces back to ignition, air metering, vacuum leaks, or timing-related faults before it becomes a full misfire complaint.
A check-engine light is a graph entry point into code pages, symptom-specific diagnosis, and the exact repair categories most often associated with those failures.
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Related Codes
General fault with the upstream O2 sensor on bank 1. This sensor monitors exhaust oxygen to control fuel mixture.
The engine is running lean on bank 1 — too much air or not enough fuel. The ECM has maxed out its fuel trim trying to compensate. Common causes include vacuum leaks and dirty MAF sensors.
Upstream O2 sensor on bank 1 is stuck at high voltage, indicating a rich condition.
Frequently Asked Questions
- 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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Author & Review
Written by AllOEMManuals Editorial Team. Reviewed by ASE-certified technicians and updated with factory-reference checks for fitment-sensitive steps.
This guide was drafted with AI assistance and reviewed for accuracy by a human editor.
Last updated: 2026-05-07