P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
Key takeaways
- P0137 means the downstream oxygen sensor on bank 1, the one after the catalytic converter, is reading lower voltage than it should for too long.
- It is safe to drive; the downstream sensor only checks the converter and does not control the fuel mixture on most cars.
- An exhaust leak ahead of the sensor, damaged wiring, and a worn-out sensor are the usual causes; a new sensor runs $150–$400.
- Only 10 complaints filed with NHTSA mention P0137, but 58 manufacturer bulletins name it, several blaming software, oil contamination or the sensor itself.
What P0137 means
The oxygen sensor behind your catalytic converter is reporting a signal that stays too low. Scanners call it O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2). Bank 1 is the side of the engine with cylinder 1 (a four-cylinder has only bank 1), and sensor 2 is the downstream sensor after the converter. A healthy downstream sensor reads a fairly steady voltage in the middle of its range; a low reading means it is seeing lean exhaust (extra oxygen) or its signal wire is being pulled low. When the computer sees that for longer than it allows, it sets P0137.
Is it safe to drive?
Yes. On most cars the downstream sensor only watches the converter; it does not decide how much fuel the engine gets, so the car drives normally. Book a repair in the next few weeks, since a lit check engine light fails emissions inspections in most states and hides any new code. The answer changes if the car also runs rough, the light flashes, or you get lean codes like P0171: then the problem is upstream and the P0137 is just a symptom.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Exhaust leak ahead of the sensor | Ticking at cold start, soot at a joint; smoke test of the exhaust | $150–$600 |
| Damaged wiring or connector | Melted or chafed wire near the exhaust, corroded plug; voltage drops when wiggled | $100–$250 |
| Worn or contaminated sensor | Circuit tests good but the sensor stays low and lazy on a scan tool | $150–$400 |
| Oil leaking onto the sensor | Oil on the sensor or exhaust from a valve cover or other leak above it | $150–$500 for the gasket, plus $150–$400 for the sensor if needed |
| Software fault | Matching bulletin for your vehicle | $100–$200, often $0 under warranty |
| Engine actually running lean | Lean codes, high fuel trims; the sensor is telling the truth | Depends on the cause; start with a vacuum leak |
What to check first
- Look for other codes. P0137 with P0141 (heater circuit) or lean codes changes the plan.
- Watch the sensor on a scan tool at warm idle and at 2,500 rpm. A dead-flat low reading while the upstream sensor switches normally points to the sensor or wiring.
- Check for exhaust leaks between the engine and the sensor. Outside air pulled in at a leak reads as lean.
- Inspect the wiring along the exhaust for heat or rodent damage.
- Check for bulletins before buying a sensor.
- Clear it and drive. After a repair, clear the code and drive a few days to confirm it stays off.
The bulletins show real patterns. Subaru released new downstream sensors for the 2020–2023 Outback. Jeep traced some 2018–2021 Wrangler and Gladiator codes to oil from the bank 1 valve cover seal leaking onto the downstream sensor. GM traced some 2014–2018 Silverado, Sierra and Escalade cases to a software anomaly. Ford has bulletins for the 2016 C-MAX, Fusion and MKZ hybrids, the 2019–2020 Edge and Nautilus 2.0L, and the 2018–2019 EcoSport.
What it costs
The cheap outcome is a wiring repair at $100–$250 or an exhaust gasket at $150–$600. The common outcome is a new downstream sensor, $150–$400. The expensive outcome is fixing an oil leak above the sensor and replacing the contaminated sensor, up to about $900. An hour of diagnosis, usually $100–$180, tells you whether the sensor is lying or telling the truth before you buy one. Not sure which sensor is which on your car? Ask our AI mechanic.
Related codes
P0137 often shows with P0138 (the same sensor reading high) or P0141 (its heater). With P0420, check the converter and the sensor together. For a wider look at O2 codes, see O2 sensor check engine light.
What owners report to NHTSA
10 complaints filed with NHTSA mention P0137, 8 of them since 2015, across 8 different models. The component owners most often filed it under: fuel/propulsion system.
Manufacturer service bulletins that name P0137
58 technical service bulletins and manufacturer communications filed with NHTSA mention P0137, from 14 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- SUBARU OUTBACK (2020, 2021, 2022, 2023), bulletin 11000828: This bulletin announces the availability of new oxygen sensors developed to address the following Diagnostic Trouble Codes (DTCs); P0137 (O2 Sensor Circuit Low Voltage Bank 1 Sensor 2, P0138 (O2 Sensor Circuit High Volta…
- JEEP WRANGLER (2018, 2019, 2020, 2021), bulletin 10212474: Customer?s complaint may include a MIL-on with one or more of the following DTCs Active, Pending, or Stored in the PCM: P0133, P0137, P0171, P0300, P2096. The root cause could be due to oil leaking from Bank 1 valve cove…
- JEEP GLADIATOR (2020, 2021, 2018, 2019), bulletin 10218493: Customer?s complaint may include a MIL-on with one or more of the following DTCs (Active, Pending, or Stored) in the PCM: P0133, P0137, P0171, P0300, P2096. The root cause could be due to oil leaking from Bank 1 valve co…
- FORD EDGE (2019, 2020), bulletin 10202794: Some 2019-2020 Edge/Nautilus vehicles equipped with 2.0L EcoBoost engine and built on or before 14-Oct-2020 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs) P0137, P0141 an…
- LINCOLN NAUTILUS (2019, 2020), bulletin 10202794: Some 2019-2020 Edge/Nautilus vehicles equipped with 2.0L EcoBoost engine and built on or before 14-Oct-2020 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs) P0137, P0141 an…
- FORD ECOSPORT (2018, 2019), bulletin 10153918: Some 2018-2019 EcoSport vehicles equipped with a 2.0L Duratec engine and an automatic transmission and built on 1-Sep-2017 and through 28-Nov-2018 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnost…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can I drive with a P0137 code?
Yes. The sensor after the converter doesn't run the engine, so the car drives the same. Fix it before your next emissions test, because the light will fail an inspection and it hides any new code that sets.
Where is bank 1 sensor 2?
Bank 1 is the side of the engine with cylinder 1; on a four-cylinder there is only one bank. Sensor 2 is the one after the catalytic converter, usually under the car behind the converter.
Is P0137 a bad catalytic converter?
Usually not. A failing converter normally sets P0420. P0137 is about the sensor's voltage staying low, which points to the sensor, its wiring, or outside air leaking into the exhaust ahead of it.
Will a new O2 sensor fix P0137?
Only if the sensor is the problem. Check for exhaust leaks and wiring damage first. If the code comes back quickly after a new sensor, look for a leak or a bulletin for your car.