P0138 Code: O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)


There are more than fifty things that can affect the performance of your vehicle and illuminates the check engine light. These lights are a part of the OBD-II system and can indicate P0138 Code the faults in the components of the vehicles.

Definition of P0138 error code

The P0138 error code states as O2 Sensor Circuit High Voltage (Bank 1, Sensor 2).

Meaning of P0138 error code

Oxygen sensor 2 is the rear oxygen sensor that is connected with the catalytic converter. It measures the quantity of the air and fuel that is emitted by the catalytic converter to inspect its functioning. The voltage is the primary factor that decides the sound working of the catalytic converter.


If the voltage is high, it indicates that the quantity of fuel is more in the mixture. The low voltage indicates the high quantity of air in the mixture. Hence, the rear oxygen sensor should generate a precise voltage of approximately .45 volts.
When the check engine light illuminates and triggering the P0138 error code, it implies that high voltage is flowing for more than 10 seconds and it also indicates that there is a lack of oxygen in the exhaust stream and enough fuel is present in sensor 2 on the bank 1of the engine.

Possible causes of the P0138 error code

Many factors can trigger the P0138 error code. Some of them are:

  • Defects or faults in O2 Sensors
  • Defects in air-fuel sensor
  • Defects in wiring
  • Faults in the connection to the oxygen sensor
  • Excessive fuel pressure
  • Corrosion in wiring
  • Shorting in wires
  • Clogged catalytic converter
  • Leaking fuel injector

Symptoms of the P0138 error code

These are the symptoms that are visible in the vehicle when your vehicle is triggered with the P0138 error code:

  • The engine may run lean during sensor testing
  • Hesitation on acceleration
  • The engine of the vehicle may lag or miss
  • Fuel economy fails
  • The vehicle goes on Rough idle condition
  • Engine dies or problem in starting
  • Foul fumes emitted
  • Check engine light illuminates

The seriousness of the P0138 error code

While driving in a short distance while your car is diagnosed with the P0138 error code, it will not create any problem. But you should detect the actual reason for the error code. This error code directly affects the fuel efficiency of the vehicle and this will affect the exhaust of the system. Running with a rich engine can directly affect the efficiency of the car.

How to check the P0138 error code?

When your vehicle is diagnosed with the P0138 error code, and to inspect the oxygen sensors bank 1 sensor, you need to follow these steps:

Check the corroded terminals: inspect the connecting wires from oxygen sensors to the catalytic converter, if they are corroded, shorted, or damaged.

Check the fouling of the sensor2: fouling is the indication for more fuel than oxygen in the air-fuel mixture. If your oxygen sensor contains more fuel than the oxygen it will emit a strong weird smell. Leakage on the exhaust system is also a primary reason for the fouling smell in the oxygen sensor.


Check the electrical connections: inspect the damages and cracks in the exhaust pipes and the catalytic converter. Check if the wiring harnesses are in the good condition or they melt because of the closeness of warm exhaust parts. Check visually for the connections as well as using Ohm meter.

How to fix the diagnosed P0138 error code?

If your vehicle is diagnosed with P0138 error code, you need to diagnose the defective component that triggers the check engine light on because of P0138 error code.
Mostly the primary cause of the P0138 error code is the faults in the oxygen sensors. Check it or replace it. These faults can occur because of the wire connections, also inspect for the burnt, and damage wires of the oxygen sensors.
If there is a requirement for the replacement of the catalytic converter, do it. The leakage of the fuel injector should also be repaired.

Some other tips for troubleshooting the P0138 error codes are:

Clear the codes that are stored in the ECU and take a small test drive to check the voltage of the oxygen sensors. If the sensors go in high voltage this indicates that there are some faults in the oxygen sensors, and they need replacement.
If you are facing some issues of fuel efficiency, in your vehicle and your vehicle is triggered with the P0138 error code, then you must visit a mechanic and should check the defective components of the vehicle.

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