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.
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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
Step-by-Step Diagnostic Procedure
-
Check downstream O2 voltage. Stuck below 0.2V consistently indicates lean bias or a circuit fault.
-
Inspect exhaust system for leaks between the catalyst and the sensor.
-
Check signal wiring for ground shorts.
-
If fuel trims are also lean (positive values), investigate the underlying lean condition first.
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 Denso 234-4350. 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.
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 Motorcraft DY-1178. Check for exhaust leaks between the catalytic converter and the sensor which dilute the exhaust sample and cause false low readings.
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 213-4573). Use penetrating oil for 24 hours before attempting removal. Also check the catalytic converter for internal damage with a back-pressure test.
Labor: 30 min2008-2019 Honda Accord/CR-V 2.4L easy DIY
Honda downstream O2 sensors last about 120-150K miles. Replace with Denso 234-4350 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.
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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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