P0137: The downstream oxygen sensor on the driver side is reading too low
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
The downstream oxygen sensor voltage is too low (bank 1). Get it checked within a week or two. A stuck reading can set a false catalytic converter code, so fix this first.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
The downstream oxygen sensor on Bank 1 should oscillate slowly between about 0.1 and 0.9 volts. P0137 means it stayed below 0.1 volts longer than the computer expected. A healthy converter produces a fairly steady low-oxygen signal downstream. A reading stuck at low voltage usually means the sensor is responding only to lean exhaust, has contaminated its sensing element, or has a wiring problem pulling its signal to ground. The non-obvious point: a sensor stuck low can fool the computer into thinking the catalytic converter is working perfectly when it may not be.
Common causes
- Worn or contaminated downstream O2 sensorOil ash, coolant, or just age degrades the sensing element. The sensor gets stuck near zero.
- Lean exhaust condition at the converter outletAn exhaust leak upstream of the sensor pulls in air and keeps the sensor reading low.
- Short to ground in the signal wireDamaged insulation on the signal wire can pin the voltage low regardless of sensor condition.
- Open in the sensor reference voltage wireIf the PCM reference voltage is not reaching the sensor, output stays at zero.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Wiring or connector repair
- Downstream O2 sensor (Bank 1)
Symptoms
- Check engine light on, steady
- Usually no drivability symptoms
- Possibly missing a related P0420 that would otherwise be set
- Failed emissions test
What to do next
Check for exhaust leaks between the upstream sensor and the downstream sensor first. A leak is easy to diagnose and cheap to fix. If no leak, inspect the connector and harness. If both check out, replace the sensor. Do not assume P0420 is absent because this code is set; a stuck-low sensor can suppress that code.
Lewis reads P0137 alongside any related oxygen sensor codes and shows your live fuel trims, so you can see whether the engine is running lean or the sensor is at fault. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is P0137 the same as P0136?
- No. P0136 is a general circuit fault. P0137 is a specific voltage-too-low fault. P0137 often points to the sensor element or a wiring short to ground, while P0136 can also mean an open circuit.
- Can a catalytic converter cause P0137?
- A very efficient, new converter keeps downstream oxygen low, but not low enough to trigger this code under normal conditions. If anything, P0137 can mask a failing converter.
- Will cleaning the sensor fix it?
- Rarely. Oxygen sensors are not serviceable. If the element is contaminated, the sensor needs replacement.
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