P0131: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
Moderate SeveritySafe to drive (short-term)Emissions
P0131 means the upstream oxygen sensor on bank 1 is consistently reporting a low voltage, indicating a lean exhaust condition. The ECU may compensate by adding extra fuel, causing rich running. This code often points to a failing O2 sensor or an actual lean condition.
What does P0131 mean?
P0131 means the upstream oxygen sensor on bank 1 is consistently reporting a low voltage, indicating a lean exhaust condition. The ECU may compensate by adding extra fuel, causing rich running. This code often points to a failing O2 sensor or an actual lean condition.
P0131 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0131 and illuminates the check engine light.
What are the symptoms of P0131?
If your vehicle has triggered P0131, you may notice one or more of these symptoms:
Check engine light on
Increased fuel consumption
Rough idle or engine hesitation
Possible sulfur or rotten egg smell from exhaust
Failed emissions test
Sluggish acceleration
What causes P0131?
Here are the most common causes of P0131, ranked by how likely they are to be the culprit:
highFailing or aged oxygen sensor (bank 1, sensor 1)
highVacuum leak causing actual lean condition
mediumExhaust leak before the O2 sensor
mediumDamaged or corroded O2 sensor wiring/connector
lowContaminated O2 sensor (coolant or silicone exposure)
Generally yes, for short-term driving. You can drive to a workshop, but the engine may run rich, increasing fuel consumption and potentially damaging the catalytic converter over time. Do not delay repairs for more than a few days.
How do you diagnose P0131?
Follow these steps to pinpoint the root cause of P0131:
Use a scan tool to monitor the bank 1 sensor 1 O2 voltage in real time. A healthy sensor oscillates between 0.1V and 0.9V. A stuck-low reading (below 0.2V) suggests a lean condition or sensor failure
Check for vacuum leaks by performing a smoke test or spraying propane around intake manifold gaskets, vacuum hoses, and the brake booster line. A leak causes real lean conditions
Inspect the exhaust system between the engine and the O2 sensor for leaks. Cracked exhaust manifolds or loose connections allow outside air to reach the sensor, giving false lean readings
Inspect the O2 sensor connector and wiring for corrosion, heat damage, or rodent chewing. Repair any wiring faults found
If no leaks or wiring issues are found, replace the O2 sensor. Sensors degrade over time and should be replaced every 100,000-150,000 km as maintenance
How much does P0131 cost to fix?
Repair costs for P0131 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace O2 sensor (bank 1, sensor 1)
€30–€150
€40–€120
€70–€270
Moderate
Fix vacuum leak
€10–€60
€40–€150
€50–€210
Moderate
Repair exhaust leak before O2 sensor
€15–€80
€50–€200
€65–€280
Moderate
Repair O2 sensor wiring
€5–€25
€40–€120
€45–€145
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0131 on specific vehicles
P0131 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0131 on Toyota Corolla
Toyota Corolla • 2005-2024
The 1ZR-FE and 2ZR-FE engines are reliable, but O2 sensors typically need replacement around 120,000-150,000 km. Use a Denso sensor (OE supplier) for best compatibility. The upstream sensor is easily accessible on the exhaust manifold.
What causes P0131 on a Toyota Corolla?
Toyota CorollaO2 sensor degradation at high mileage
Toyota CorollaExhaust manifold cracking on older models causing false lean readings
P0131 repair cost for Toyota Corolla
Estimated costs for Toyota Corolla ownersadjusted lower than average due to Toyota-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace O2 sensor (bank 1, sensor 1)
€27–€135
€36–€108
€63–€243
Moderate
Fix vacuum leak
€9–€54
€36–€135
€45–€189
Moderate
Repair exhaust leak before O2 sensor
€14–€72
€45–€180
€59–€252
Moderate
Repair O2 sensor wiring
€5–€23
€36–€108
€41–€131
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0131 on Volkswagen Golf
Volkswagen Golf • 2005-2024
The EA888 2.0 TSI and 1.4 TSI engines use wideband (AFR) sensors rather than traditional narrowband O2 sensors. These are more expensive to replace. Vacuum leaks from the PCV system or intake manifold are common triggers on turbo engines.
What causes P0131 on a Volkswagen Golf?
Volkswagen GolfPCV valve failure causing vacuum leak and lean condition
Volkswagen GolfWideband O2 sensor degradation on EA888 engines
P0131 repair cost for Volkswagen Golf
Estimated costs for Volkswagen Golf ownersadjusted higher than average due to Volkswagen-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace O2 sensor (bank 1, sensor 1)
€35–€173
€46–€138
€81–€311
Moderate
Fix vacuum leak
€12–€69
€46–€173
€57–€241
Moderate
Repair exhaust leak before O2 sensor
€17–€92
€57–€230
€75–€322
Moderate
Repair O2 sensor wiring
€6–€29
€46–€138
€52–€167
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0131 on Honda Civic
Honda Civic • 2006-2024
Honda Civics with the R18A engine commonly trigger P0131 from O2 sensor aging around 130,000 km. The 1.5L turbo (L15B7) can develop vacuum leaks at the turbo inlet pipe, causing real lean conditions that trigger both P0131 and P0171.
What causes P0131 on a Honda Civic?
Honda CivicO2 sensor wear on R18A engines at high mileage
Honda CivicTurbo inlet pipe leak on 1.5T causing lean condition
P0131 repair cost for Honda Civic
Estimated costs for Honda Civic ownersadjusted lower than average due to Honda-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace O2 sensor (bank 1, sensor 1)
€29–€143
€38–€114
€67–€257
Moderate
Fix vacuum leak
€10–€57
€38–€143
€48–€200
Moderate
Repair exhaust leak before O2 sensor
€14–€76
€48–€190
€62–€266
Moderate
Repair O2 sensor wiring
€5–€24
€38–€114
€43–€138
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
These codes are often seen alongside P0131 or indicate related issues:
P0131 means the upstream oxygen sensor on bank 1 is reading low voltage consistently, which the ECU interprets as a lean exhaust condition. This sensor is critical for fuel mixture control - when it fails, the engine cannot properly regulate the air-fuel ratio.
Can I drive with P0131?
Yes, for short distances. The ECU compensates by richening the fuel mixture, which increases fuel consumption and can damage the catalytic converter over time. Schedule a repair within a few days to prevent secondary damage.
How long does an O2 sensor last?
Most modern oxygen sensors last 100,000 to 150,000 km. However, exposure to coolant leaks, silicone sealants, or contaminated fuel can shorten their lifespan significantly. If your vehicle has high mileage and the original sensors, age is the likely cause.
Is P0131 the same as P0171?
No. P0131 specifically indicates the O2 sensor circuit is reading low voltage (a sensor-side problem). P0171 indicates the fuel system is actually running lean based on long-term fuel trims. However, both can appear together if there is a real lean condition.
