P0137O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The oxygen sensor after the catalytic converter on bank 1 (sensor 2) is a switching sensor (about 0.1–0.9 V) used for converter monitoring and fine mixture trim. P0137 means the signal stays below the lower limit. Documented limits: GM below 40–60 mV (two trips); Ford switches in a pull-up and reads open above 1 MΩ (20 kΩ from 2020) or short to ground below 10 Ω, within 10 s. Subaru uses the code as a functional test instead: the sensor never reaches 550 mV within 200 s after fuel cut-off, i.e. it behaves as if permanently lean – so a real exhaust leak can also trigger it there. When it fails, the control module stops the downstream trim and cannot evaluate the converter; there is no limp mode.
- What you may notice
- Check engine light on (usually after two drive cycles)
- Catalyst monitor readiness not set
- Usually no noticeable change in driving
- Likely causes
- LikelySignal wire shorted to ground or melted against the exhaust
- LikelySensor faulty (cracked element, thermal shock from water)
- PossibleSignal circuit open (counts as low on Ford)
- PossibleExhaust leak ahead of the sensor (lean reading)
- RareSignal and ground wires swapped after a repair
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.