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

An oxygen sensor circuit issue was detected.

Code Overview

An oxygen sensor circuit issue was detected.

Common Causes

• Failing upstream oxygen sensor on bank 1 sensor 1
• Exhaust leak ahead of the sensor
• Wiring fault or poor terminal contact in the sensor circuit
• Actual lean-running condition on bank 1

Symptoms

• Check-engine light with lean fuel trims
• Rough idle or hesitation
• Poor fuel economy or drivability complaint

Diagnostic Steps

1. Check fuel trims, misfire codes, and exhaust leaks before condemning the sensor
2. Inspect the bank 1 sensor 1 harness near the exhaust for damage
3. Watch upstream sensor switching and voltage behavior on the scan tool
4. Verify the circuit and confirm the engine is not actually running lean

Repair Difficulty

Moderate

General difficulty estimate for the most common repair path.

Likely Repairs & Cost Guides

Use test results to confirm the fault before pricing the repair.

Related OBD Codes

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Next Steps

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