P0159 OBD-II Trouble Code: Oxygen Sensor (Bank 2, Sensor 2)

P0159 – technical description

Oxygen (O2) sensor response (bank 2, sensor 2)

What does DTC P0159 mean?

Code P0159 is a transmission code that indicates a problem with a specific sensor in the exhaust system (bank 2, sensor 2). If the oxygen sensor is slow, it may be a sign that it is faulty. This particular sensor is responsible for monitoring catalyst efficiency and emissions.

This Diagnostic Trouble Code (DTC) is generic for the transmission and applies to vehicles with the OBD-II system. Despite the general nature of the code, the specifics of the repair may vary depending on the make and model of the vehicle. We are talking about the rear oxygen sensor on the right passenger side. “Bank 2” refers to the side of the engine that does not have cylinder #1. “Sensor 2” is the second sensor after leaving the engine. This code indicates that the engine is not regulating the air/fuel mixture as expected by the ECM or the oxygen sensor signal. This can happen both while the engine is warming up and during normal operation.

What are the symptoms of trouble code P0159

You may not notice any problems with your vehicle's handling, although some symptoms may occur.

Check Engine Light: This light's primary function is to measure emissions and does not have a significant impact on vehicle performance.

This sensor is a downstream oxygen sensor, meaning it is located after the catalytic converter. The computer uses the lower oxygen sensors to evaluate the performance of the catalyst and the upper sensors to calculate the fuel-air mixture.

Causes of Code P0159

The P0159 code may indicate one or more of the following:

1. The oxygen sensor is faulty.
2. Damage or chafing of the sensor wiring.
3. Presence of exhaust gas leak.

This code sets if the oxygen sensor modulates slowly. It should oscillate between 800 mV and 250 mV for 16 cycles over 20 seconds. If the sensor does not meet this standard, it is considered faulty. This is usually due to age or contamination of the sensor.

Exhaust leaks can also cause this code. Despite popular belief, an exhaust leak sucks in oxygen and dilutes the exhaust flow, which can be interpreted by the computer as a faulty oxygen sensor.

The sensor has four wires and two circuits. If one of these circuits is shorted or has high resistance, it may also cause this code to set as such conditions can affect the performance of the oxygen sensor.

How to diagnose code P0159?

Technical Service Bulletins (TSBs) are worth checking for specific problems related to the make and model year of your vehicle.

This code is set by the computer after running certain specific tests. Therefore, a technician who has diagnosed a vehicle and found this code will typically check for exhaust leaks before replacing the said sensor (Bank 2, Sensor 2).

If more detailed testing is required, there are several ways to perform it. A technician can directly access the oxygen sensor circuit and observe its operation using an oscilloscope. This is usually done while introducing propane into the intake or creating a vacuum leak to monitor the oxygen sensor's response to changing conditions. These tests are often combined with a test drive.

Resistance tests can be performed by disconnecting the oxygen sensor connector from the vehicle wiring. This is sometimes done by heating the sensor to simulate the conditions it will experience when installed in the exhaust system.

Diagnostic errors

Failure to identify other problems such as exhaust leaks, vacuum leaks or misfires is not uncommon. Sometimes other problems may go unnoticed and can be easily missed.

Downstream oxygen sensors (oxygen sensors after the catalytic converter) are designed to help ensure your vehicle meets EPA exhaust emission standards. This oxygen sensor not only monitors the efficiency of the catalyst, but also performs tests to verify its own effectiveness.

The rigorous nature of these tests requires that all other systems operate correctly or the results may be inaccurate. Therefore, eliminating most other codes and symptoms should be considered first.

How serious is trouble code P0159?

This code has little impact on daily driving. This is not a problem that would require calling a tow truck.

The introduction of such systems was prompted by the serious problem of global warming and was done by the Environmental Protection Agency in conjunction with the automobile industry.

What repairs will correct the P0159 trouble code?

The simplest step is to reset the code and check if it comes back.

If the code returns, the problem is likely with the passenger side rear oxygen sensor. You may need to replace it, but also consider the following possible solutions:

1. Check and repair any exhaust leaks.
2. Check the wiring for problems (short circuits, frayed wires).
3. Check the frequency and amplitude of the oxygen sensor signal (optional).
4. Check the condition of the oxygen sensor; if it is worn or dirty, replace it.
5. Check for air leaks at the intake.
6. Check the performance of the mass air flow sensor.

The most common solution would be to replace the said oxygen sensor (bank 2, sensor 2).

Repair exhaust leaks before replacing the oxygen sensor.

Damaged wiring in the oxygen sensor circuit can be detected and should be repaired. These wires are usually shielded and require special care when connecting.

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Additional comments regarding error code P0159

Bank 1 is the set of cylinders that contains cylinder number one.

Bank 2 is a group of cylinders that does not include cylinder number one.

Sensor 1 is the sensor located in front of the catalytic converter that the computer uses to calculate the fuel ratio.

Sensor 2 is a sensor located after the catalytic converter and is primarily used to monitor emissions.

In order for the vehicle to test the functionality of Sensor 2, the following conditions must be met. This fault detection method may vary between manufacturers and is applicable under the following conditions:

1. The car travels at speeds between 20 and 55 miles per hour.
2. The throttle is open for at least 120 seconds.
3. Operating temperature exceeds 70℃(158℉).
4. The catalytic converter temperature exceeds 600℃ (1112℉).
5. The emission evaporation system is turned off.
6. The code is set if the oxygen sensor voltage changes less than 16 times from rich to lean with an interval of 20 seconds.

This test uses two phases of fault detection.