P0156 trouble code definition
Oxygen Sensor Circuit Malfunction (Bank 2 Sensor 2)
What the P0156 code means
The purpose of the oxygen sensor is to monitor the amount of oxygen present in the exhaust and relay this information to the power control module (PCM). As the amount of oxygen increases or decreases, the oxygen sensor fluctuates between a low voltage and a high voltage.
If the oxygen sensor remains at a low voltage for an extended period of time, or is simply not active at all, the P0156 trouble code will be stored by the power control module (PCM) and the Check Engine Light will come on as an indication to the driver that there is a problem in the engine.
What causes the P0156 code?
- Gas leaks in the exhaust
- Air leaks in the intake
- Defective fuel injectors
- Broken or exposed wires
- Voltage wires or circuits that have shorted out
- Exhaust holes that are located near or around the oxygen sensor
- Engine vacuum leaks
- Oxygen sensor wires touching the exhaust
What are the symptoms of the P0156 code?
Drivers may not notice any symptoms associated with the P0156 trouble code. The Check Engine Light will come on, which is the most noticeable symptom, and there may be a loss of fuel economy. The vehicle will also have an increase of pollutants that it is emitting into the environment.
How does a mechanic diagnose the P0156 code?
An OBD-II scanner is used to make a record of all trouble codes that have been stored by the power control module (PCM).
The oxygen sensor live data on the OBD-II scanner is reviewed to make an observation as to whether the oxygen sensor is working properly.
They will be able to make a conclusion by noting whether the oxygen sensor is switching from low voltage to high voltage as it should.
Using the OBD-II scanner, they will view live data for the fuel injectors to make sure they are working properly.
The oxygen sensor wiring will be inspected for shorted, broken, or exposed wires.
The engine will be checked for escaping air. This could be an indication of vacuum leaks or broken vacuum lines and then exhaust will be inspected for holes.
Common mistakes when diagnosing the P0156 code
The mistake that is most commonly made when diagnosing the P0156 trouble code is automatically replacing the oxygen sensor without inspecting any other component. The oxygen sensor is not always the problem, and replacing it does not always remedy the problem.
Consideration should be given to the condition of the wiring, exhaust, vacuum lines, intake and fuel injectors.
How serious is the P0156 code?
This code is not generally considered a serious one. However, the driver may experience an increase of fuel consumption and while in this condition, and the vehicle will let off more pollutants into the environment.
What repairs can fix the P0156 code?
- Repairing shorted, broken, or exposed oxygen sensor wires
- Repairing vacuum leaks
- Repairing holes in the exhaust or replace exhaust, if necessary
- Replacing the fuel injector, if faulty
- Replacing the oxygen sensor (bank 2 sensor 2)
Additional comments for consideration regarding the P0156 code
At times, depending on the vehicle, the oxygen sensor may be hard to reach. An oxygen sensor set may be needed to remove the sensor. It is also common for the oxygen sensor to cease up in the exhaust and to be removed properly by a heating element, such as a propane torch, in addition to the oxygen sensor set.
Need help with a P0156 code?
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This article originally appeared on YourMechanic.com as P0156 OBD-II Trouble Code: 02 Sensor Circuit Malfunction (Bank 2 Sensor 2) and was authored by Jamahl Walker.