O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
The P0137 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $50-$450 (DIY budget part at the low end; shop replacement of the downstream sensor with a quality part at the high end)
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
Shows real-time O2 sensor readings on your phone. See if the sensor is lazy, stuck, or actually working before spending money.
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Common Symptoms
- Check Engine Light on
- Engine may run lean
- False lean trim readings
- Possible P0171 combination
Probable Causes (Ranked by Likelihood)
- O2 sensor stuck lean (low voltage output) Very High
- Exhaust leak pulling in fresh air near sensor High
- Short to ground in signal wire Moderate
- Genuine lean running condition Moderate
Common Fixes by Vehicle
What techs usually find when diagnosing P0137 on specific vehicles — tap your vehicle for the fix and the exact part:
2007-2017 Toyota Camry/Corolla 2.5L easy DIY
Bank 1 Sensor 2 (downstream) O2 sensor is reading below 0.2V consistently. This sensor monitors catalyst efficiency. Replace with an OE-quality Denso unit. Before replacing, check the sensor wiring for heat damage from the catalytic converter. If P0420 is also present, the catalyst may be failing and contaminating the sensor. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30 min2009-2020 Ford F-150/Explorer 3.5L/5.0L easy DIY
Test the downstream O2 sensor voltage with a scan tool -- it should fluctuate slowly between 0.1V and 0.9V. If stuck low, the sensor has failed. Replace with an OE-quality Motorcraft unit. Check for exhaust leaks between the catalytic converter and the sensor which dilute the exhaust sample and cause false low readings. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30-45 min2010-2020 Chevrolet Silverado/Tahoe 5.3L easy DIY
Downstream O2 sensor on Bank 1 (driver side) reading low voltage. Check for broken exhaust manifold bolts causing a leak -- very common on GM trucks. If no leaks, replace the sensor (ACDelco). Use penetrating oil for 24 hours before attempting removal. Also check the catalytic converter for internal damage with a back-pressure test. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30 min2008-2019 Honda Accord/CR-V 2.4L easy DIY
Honda downstream O2 sensors last about 120-150K miles. Replace with an OE-quality Denso unit for exact OE fit. Before replacing, verify the sensor is getting proper ground by testing the connector. Also check the exhaust pipe gasket between the catalytic converter and the sensor bung for leaks. A leaking gasket causes erratic low-voltage readings. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30 minFrequently Asked Questions
Can an exhaust leak after the catalytic converter cause P0137?
Yes. Fresh air pulled into a small exhaust leak dilutes the exhaust gases near the sensor, causing a lean (low voltage) reading that is not representative of actual catalytic converter function.
What actually makes the computer set an oxygen sensor code?
The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Check downstream O2 voltage. Stuck below 0.2V consistently indicates lean bias or a circuit fault.
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Inspect exhaust system for leaks between the catalyst and the sensor.
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Check signal wiring for ground shorts.
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If fuel trims are also lean (positive values), investigate the underlying lean condition first.
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- Honda Accord and Odyssey
- Toyota 4Runner
- Ford Explorer
- Chevrolet Suburban
- Nissan Pathfinder
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