OBD-II Code · Sensors
P0137
O2 Sensor Low Voltage (B1S2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Downstream sensor reading low.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Failed sensorMost common
- Exhaust leak
- Wiring short
Read the full diagnostic procedureP0137 says bank 1 downstream (B1S2) signal is stuck LOW — under ~0.1V on a narrow-band.
P0137 says bank 1 downstream (B1S2) signal is stuck LOW — under ~0.1V on a narrow-band. On a healthy car the downstream sensor sits relatively flat at 0.6-0.8V because the cat consumes the free O2; a signal pinned near zero means the sensor is reading 'lots of oxygen' constantly.
That can mean three things
real lean exhaust at the post-cat position (exhaust leak between the cat and the sensor letting atmosphere in), a failed cat that no longer consumes oxygen (in which case you'll usually see P0420 set too), or a bad sensor / wiring fault pulling the signal to ground. Cheapest-first: visually + audibly check for exhaust leaks between the cat outlet and the downstream sensor bung — small pinholes from rust on the flex pipe or cat outlet are very common on northern cars. If the exhaust is sealed, scan upstream B1S1 — if it's switching normally and fuel trims are good, the cat OR the downstream sensor is the issue; swap B1S2 with a known-good unit before condemning the cat.
Vehicle-specific patterns1999-2006 Chevy Silverado / Tahoe 5.3L LM7 throws P0137 from rusted-out flex pipe between the cat and the downstream sensor — fix the leak, not the s…
- 1999-2006Chevy Silverado / Tahoe 5.3L LM7 throws P0137 from rusted-out flex pipe between the cat and the downstream sensor — fix the leak, not the sensor.
- 2004-2010Toyota Sienna / Highlander 3.3L 3MZ-FE sets P0137 when the downstream connector wicks moisture through the strain relief; dry + dielectric grease often clears it.
- 2007-2012Nissan Altima / Maxima VQ35 throws P0137 from a defective Bosch downstream sensor lot — Nissan TSB acknowledged.
- 2005-2012Ford Escape / Mariner Hybrid sets P0137 when the cat itself fails (you'll see P0420 alongside) — hybrid cats run cooler and degrade faster than ICE-only equivalents. Cost band: $150-$350 for sensor; $200-$600 if a flex-pipe weld is the real cause; $1,000+ if the cat actually failed.
Look up another code
P0137 — frequently asked
What does a P0137 code mean?
Downstream sensor reading low.
What causes a P0137 code?
Common causes: Failed sensor; Exhaust leak; Wiring short.
What are the symptoms of a P0137 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0137 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0137 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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