OBD codes / P0137
P0137
ModerateO2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
Driving with P0137 is low-risk — the rear sensor does not control the engine, so the car runs normally. There is no urgency beyond emissions compliance, but do not simply clear the code repeatedly: a small exhaust leak behind the converter, one of the possible causes, tends to grow louder and more expensive over time.
What this code means
P0137 means the downstream oxygen sensor on Bank 1 — the one after the catalytic converter — is reporting a voltage stuck low for too long. Downstream of a healthy converter the signal is normally fairly steady and moderately high, so a persistently low reading suggests either a real problem or a bad signal path. The most common culprits are a failing sensor, a wiring short to ground, or an exhaust leak between the converter and the sensor letting outside air in, which reads as lean. A genuinely lean-running engine can also drag this signal down, in which case there are usually companion codes. Because Sensor 2 exists to monitor the catalyst rather than control fueling, this code rarely changes how the car drives — its real cost is a failed emissions test and an unreliable catalyst monitor.
Symptoms you might notice
- Check-engine light, usually the only symptom
- No noticeable drivability change
- Failed emissions test
- Companion lean or catalyst codes in some cases
What it costs to fix
Typical range: $100–$450 · about ~0.3–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Downstream oxygen (O2) sensor | $30–$250 | ~0.3–1 hrs |
| Exhaust leak repair (gasket or pipe section) | $20–$200 | ~0.5–2 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
Typically a low-hundreds repair, often at the affordable end because rear sensors tend to be accessible and cheaper than upstream ones. An exhaust leak that needs a new flange gasket or welded pipe section changes the math.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0137 for my exact vehicle →
How to fix P0137
Easy — basic tools, most owners can do this
- Hunt for an exhaust leak ahead of the sensor
Cold-start the engine and listen around the converter-to-sensor section for ticking; inspect flange gaskets and welds for soot trails. Outside air leaking in reads as lean and drags the downstream voltage low — exactly this code — with a perfectly good sensor.
- Look for companion codes before condemning the sensor
Scan for lean codes (P0171) or upstream sensor faults stored alongside. A genuinely lean-running engine pulls the downstream signal low too, and fixing the lean condition — not the rear sensor — is the real repair in that case.
- Inspect the signal wiring for a short to ground
Check the underbody harness for sections pressed against the exhaust or chassis with insulation worn away. A signal wire grounding out produces a stuck-low voltage indistinguishable from a dead sensor until you look.
- Test the sensor's response, then replace it
On live data, snap the throttle a few times — a momentary rich event should nudge the downstream voltage upward. A signal that stays flat and low through that test marks a failed sensor; replace it with an O2 socket after soaking the threads.
- Verify the voltage recovers to normal
After repair, a warm-engine downstream reading that sits steady in the healthy mid-to-high range confirms both the sensor and the signal path. Clear the code and drive enough cycles for the catalyst monitor to complete.
DIY or shop? This sits comfortably in DIY territory for anyone willing to get under the car: the leak check, wiring look-over, and sensor swap need only basic tools, and rear sensors are usually reachable. Hand it to a shop if a flange gasket or pipe section needs welding, or if companion lean codes suggest the real problem is elsewhere in the engine's fueling — chasing lean conditions benefits from a smoke machine.
Tools for the DIY steps: OBD-II scan tool with live data · O2 sensor socket · Penetrating oil · Jack stands or ramps · Flashlight
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0137.
Frequently asked
Is P0137 serious?
No — it is among the lower-urgency O2 codes because the downstream sensor only monitors the catalytic converter. The car drives normally; the main consequences are a lit check-engine light and a failed emissions test.
What is the most common fix for P0137?
Replacing the Bank 1 downstream sensor, after a quick check for exhaust leaks behind the converter and chafed wiring — both of which can imitate a bad sensor at a fraction of the cost.
What is the difference between P0137 and P0131?
Same fault, different sensor: P0131 is low voltage at the upstream sensor (which controls fueling and can affect economy), while P0137 is low voltage at the downstream sensor (which only watches the converter and rarely affects drivability).
Why did P0137 come back after replacing the sensor?
The usual suspects are an exhaust leak between the converter and sensor, a wiring short to ground, or a genuine lean condition upstream. A returning code after a new sensor almost always means the sensor was never the root cause.
Seeing P0137 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0137 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.