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P0138: Oxygen sensor (bank 1, sensor 2): voltage too high

The bank 1 oxygen sensor after the catalytic converter reads a voltage that is too high. Often a short circuit, the connector or a fouled sensor.

Code P0138 at a glance
CodeP0138
SystemEngine and transmission
GroupP01xx, Air and fuel metering
TypeGeneric: it means the same on every make
Can you keep driving?Yes, no rush

What P0138 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 ECU sees a voltage higher than is possible, usually from a short circuit or a contaminated sensor.

Most common causes

  • Damp or corroded sensor connector
  • Signal wire shorted to the heater supply wire
  • Sensor contaminated by oil, coolant or silicone
  • Mixture too rich from a leaking injector or excessive fuel pressure
  • Faulty oxygen sensor

Symptoms

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

Can you drive with P0138?

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

With the engine warm, the sensor after the converter normally gives a fairly steady voltage. If live data shows zero or an impossible fixed value, check its connector first: it sits under the car, exposed to water and dirt.

How to read and clear P0138 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 P0138 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

P0138 is a generic code, so it means the same on any make, for example on Abarth, Cupra, Jeep, Mini, Nissan, Seat. See what Final OBD does on your car in makes and models.

What does code P0138 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 ECU sees a voltage higher than is possible, usually from a short circuit or a contaminated sensor.

Can you drive with P0138?

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 P0138?

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, P0138 comes back.