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 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: 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.
Open the bonnetthe in-depth explanation
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 its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
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 an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0134 Oxygen sensor (bank 1, sensor 1): no activity
- P0135 Oxygen sensor heater (bank 1, sensor 1): circuit fault
- P0136 Oxygen sensor (bank 1, sensor 2): circuit fault
- P0137 Oxygen sensor (bank 1, sensor 2): voltage too low
- P0139 Oxygen sensor (bank 1, sensor 2): slow response
- P013A Heated lambda sensor 2 on bank 1 responds slowly when the mixture changes from
- P013B Heated lambda sensor 2 on bank 1 responds slowly when switching from lean to
- P013C Heated lambda sensor 2 on bank 2 responds slowly when switching from rich to
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Misfires, catalyst and lambda sensors.
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.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
