O2 Sensor Circuit (Bank 1, Sensor 2)
The P0136 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit (Bank 1, Sensor 2). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $50-$200
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
- Emissions test failure
- Possible false P0420 trigger
- Slight fuel economy change
Probable Causes (Ranked by Likelihood)
- Failed downstream O2 sensor Very High
- Wiring damage or connector corrosion High
- Sensor heater failure Moderate
- Exhaust leak near downstream sensor Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0136 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 circuit malfunction. The sensor monitors catalytic converter efficiency. Replace with an OE-quality Denso unit. Before replacing, check for exhaust leaks between the cat and the sensor. Also check the sensor wiring for heat damage from the catalytic converter. If P0420 is also present, the cat may be failing. 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
Bank 1 downstream O2 sensor malfunction. Check the sensor connector for heat damage -- it sits close to the catalytic converter. Test the sensor heater resistance (should be 4-8 ohms). If the heater is open, replace with an OE-quality Motorcraft unit. Also check for exhaust leaks at the cat-to-pipe connection that can contaminate the sensor reading. 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 min2008-2019 Honda Accord/CR-V 2.4L Easy DIY
Downstream O2 sensor circuit malfunction. Honda downstream sensors last about 120-150K miles. Replace with an OE-quality Denso unit. Check the sensor wiring near the catalytic converter for melted insulation. Also inspect the exhaust pipe gasket at the sensor location for leaks. Apply anti-seize to the sensor threads before installation. 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
Will a bad downstream O2 sensor cause P0420?
Yes. A lazy or slow downstream sensor mimics the waveform signature of a failed catalytic converter. Always replace or test the downstream sensor before buying a catalytic converter.
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
-
Monitor Bank 1 Sensor 2 voltage. At steady highway speed it should show a slow, mostly steady signal around 0.6-0.7V.
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If signal is erratic or shows no voltage, check wiring and connector.
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Test heater circuit resistance.
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Replace sensor if confirmed faulty.
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
- Toyota Camry and RAV4
- Honda Accord and CR-V
- Chevrolet Silverado (Bank 1 driver side)
- Ford F-150
- Nissan Altima
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