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P0139: Oxygen sensor (bank 1, sensor 2): slow response

The bank 1 oxygen sensor after the catalytic converter reacts too slowly to changes in the mixture. It is nearly always an ageing sensor.

Code P0139 at a glance
CodeP0139
SystemEngine and transmission
GroupP01xx, Air and fuel metering
TypeGeneric: it means the same on every make
Can you keep driving?Yes, no rush

What P0139 means

The oxygen sensor after the catalytic converter is mainly there to check that the converter is cleaning the exhaust properly; it has little effect on how the engine runs. This code means the signal does change, but more slowly than it should, which is typical of a sensor with high mileage.

Most common causes

  • Oxygen sensor worn out by age and mileage
  • Sensor contaminated by oil, coolant or fuel additives
  • Exhaust leak close to the sensor
  • Poor contact in the connector or wiring
  • Air leak or misfires upsetting the exhaust gases

Symptoms

  • Engine warning light on
  • The car usually drives exactly as before
  • A catalytic converter efficiency code may also appear

Can you drive with P0139?

Yes, no rush You can keep using the car normally, as this sensor has almost no effect on the engine. With the warning light on, though, it will not pass its inspection.

How to check it

While driving, lift right off the accelerator and watch the downstream sensor in live data: when the fuel cuts off, its voltage should drop quickly. If it is slow to fall, the sensor is ageing.

How to read and clear P0139 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0139 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

P0139 is a generic code, so it means the same on any make, for example on Citroën, Ford, Hyundai, Mercedes-Benz, Renault, Volvo. See what Final OBD does on your car in makes and models.

What does code P0139 mean?

The oxygen sensor after the catalytic converter is mainly there to check that the converter is cleaning the exhaust properly; it has little effect on how the engine runs. This code means the signal does change, but more slowly than it should, which is typical of a sensor with high mileage.

Can you drive with P0139?

You can keep using the car normally, as this sensor has almost no effect on the engine. With the warning light on, though, it will not pass its inspection.

How do you clear P0139?

With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0139 comes back.