P0136: O2 Sensor Circuit (Bank 1, Sensor 2) (Meaning, Causes, Fixes)
What P0136 means
Sensor 2 is the downstream oxygen sensor, mounted after the catalytic converter on bank 1 (the side of the engine with cylinder 1). OBD-Codes.com explains that an oxygen sensor produces between about 0.1 and 0.9 volts: high voltage when the exhaust is rich and low voltage when it is lean. RepairPal and OBD-Codes.com both describe P0136 as the sensor voltage staying too low (lean, below about 400 millivolts per RepairPal) for too long. OBD-Codes.com gives the set time as longer than 2 minutes, and up to 4 minutes depending on the model. Sources name the code differently: OBD-Codes.com calls it 'O2 Sensor Circuit Low Voltage' and says it is essentially the same as P0137, while RepairPal titles it 'O2 Sensor Circuit' but defines it as low voltage too, and lists P0137 separately as 'O2 Sensor Circuit Low Voltage'. Exact criteria vary by manufacturer. On some cars the upstream sensor is an air-fuel ratio sensor, and RepairPal gives separate test steps for that type.
Severity: can I keep driving?
Usually OK to drive
Get it checked within a reasonable time. RepairPal rates P0136 'Moderate', meaning it isn't usually an immediate safety risk, and OBD-Codes.com says there may be no symptoms at all. Left alone, though, it can hurt fuel economy and cause an emissions test failure. If the check engine light is flashing, the engine runs very rough, or you smell fuel or see heavy black smoke, stop driving and have it looked at, because those point to a bigger problem than this sensor. Exhaust parts get very hot, so let the car cool fully before touching the oxygen sensor.
Common symptoms
- Check engine light on
- Often no other noticeable symptoms (per OBD-Codes.com)
- Poorer fuel economy
- Rough idle or running, or a possible misfire (listed by RepairPal and OBD-Codes.com)
- Black smoke or bad-smelling exhaust, or stalling (listed by RepairPal for a faulty oxygen sensor)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Faulty bank 1 sensor 2 oxygen sensor (the most likely cause, per RepairPal)
- Exhaust leak close to the sensor
- Damaged or chafed sensor wiring, or a short in the signal circuit
- Corrosion in the connector causing high resistance
- Faulty oxygen sensor heater circuit (listed by RepairPal)
- Intake or vacuum leaks, low fuel pressure, or a bad coolant temperature sensor (listed by RepairPal)
- PCM software that needs updating, or a faulty PCM (less likely)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Read all stored codes. Fix misfire, fuel trim or vacuum leak codes first, since RepairPal lists intake leaks and low fuel pressure as possible causes.
- With the exhaust cold, find the bank 1 sensor 2 oxygen sensor just after the catalytic converter and check its wiring and connector for damage, melting, chafing or corrosion.
- Look and listen for exhaust leaks near the sensor, such as a ticking or puffing sound at a cold start, or soot around joints and gaskets.
- Clean corrosion from the connector and make sure it is fully seated.
- Clear the code and drive normally. If it comes back, the sensor or its circuit needs testing (see below).
Typical fixes
- Replace the bank 1 sensor 2 oxygen sensor
- Repair an exhaust leak near the sensor
- Repair an open or shorted signal circuit or damaged wiring
- Clean or replace a corroded connector
- Fix any vacuum leak, fuel pressure or coolant temperature sensor problem found
- Update or replace the PCM only after the sensor and wiring are confirmed good
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- Testing needs a scan tool with live data and a high-impedance multimeter. RepairPal recommends recording freeze frame data, recreating the conditions on a test drive, checking the 12-volt heater feed and grounds, back-probing the signal wire at the sensor and the PCM, and doing a wiggle test on the harness.
- RepairPal describes a lab-scope test in which a good sensor switches between under 300 and over 750 millivolts in less than 100 milliseconds, and says any reading below 0 or above 1 volt is enough to condemn the sensor
- OBD-Codes.com lists a short to voltage on the signal circuit as a possible cause, while RepairPal focuses on the sensor, heater circuit, leaks and fuel delivery. A shop can trace a wiring fault properly with a wiring diagram.
- The code returns after a new sensor, or other fuel or misfire codes are also present
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Can I drive with P0136?
Usually, for a while. RepairPal rates it 'Moderate', and OBD-Codes.com says there may be no symptoms. Get it diagnosed within a reasonable time, because it can lower fuel economy and cause an emissions test failure.
Which oxygen sensor is bank 1 sensor 2?
It is the sensor after the catalytic converter on bank 1, the side of the engine that has cylinder 1. On engines with a single exhaust, there is only bank 1.
What's the difference between P0136 and P0137?
The sources overlap. OBD-Codes.com calls P0136 'Circuit Low Voltage' and says it is essentially the same as P0137, while RepairPal titles P0136 'O2 Sensor Circuit' and lists P0137 as 'Circuit Low Voltage'. Both point to the same downstream sensor, so the checks are much the same.
Will replacing the oxygen sensor fix P0136?
Often, since RepairPal says the sensor is the most likely problem, but check for exhaust leaks near the sensor and damaged or corroded wiring first, as both sources list those as causes too.
Sources
Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.