Emission controls · Powertrain · generic (SAE-defined)
P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
P0137 means the downstream oxygen sensor after the bank 1 catalytic converter is reading lower voltage than expected, as if the exhaust is constantly lean.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0137 sets
Behind a working catalytic converter, the bank 1 sensor 2 oxygen (O2) sensor normally reports a mid-to-high, fairly steady signal. The powertrain control module (PCM) may command a brief rich condition to confirm the sensor can respond. If the signal stays low for longer than allowed, the PCM stores P0137. Thresholds are manufacturer-specific.
Common causes of P0137
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Exhaust leak ahead of the downstream sensor letting in outside air
- Failed bank 1 sensor 2 oxygen sensor
- Signal wire shorted to ground
- Damaged connector or wiring under the vehicle
- Engine running lean overall
P0137 symptoms
- Check engine light on
- Usually no drivability change
- Exhaust ticking noise if an exhaust leak is the cause
How P0137 is diagnosed
- Read codes and freeze frame; lean fuel trim codes point to a real lean mixture.
- Inspect the exhaust from the manifold to the downstream sensor for leaks, cracks or loose flanges.
- Inspect the sensor harness for damage and grounding against the body or exhaust.
- On live data, raise engine speed or add fuel briefly; the sensor should rise toward a rich reading.
- Unplug the sensor and test the signal circuit for a short to ground.
Typical fixes for P0137
- Repair exhaust leaks upstream of the downstream sensor
- Replace the bank 1 sensor 2 oxygen sensor
- Repair shorted or chafed wiring
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0137 FAQ
What does code P0137 mean?
P0137 means the downstream oxygen sensor after the bank 1 catalytic converter is reading lower voltage than expected, as if the exhaust is constantly lean. The standard definition is "O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)."
Can I drive with a P0137 code?
Yes, in most cases there is no effect on how the car runs. It should still be repaired soon because the catalyst monitor cannot work correctly and an emissions test will likely fail.
Why would an exhaust leak trigger P0137?
Outside air drawn into the exhaust adds oxygen, which makes the downstream sensor read lean. Leaks at the converter flange or a cracked pipe are frequent culprits.
Do I need a new catalytic converter for P0137?
Usually not. P0137 is about the sensor signal itself; catalytic converter faults are reported with separate efficiency codes like P0420.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.