1. Home
  2. /
  3. Complete List of OBD2...
  4. /
  5. P0159 Code – What...

P0159 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


The DTC code is an alphanumeric nomenclature used by the OBD system of a vehicle, to identify each component’s particular problems. P0159 refers to a DTC relating to an O2 sensing circuit on Bank 2, Sensor 2, and is referred to as the downstream O2 sensor. As soon as the tailpipe exhaust gases pass into a catalytic converter, this sensor will play an essential role in determining their oxygen content.


The P0159 code shows that Bank 2 is experiencing a problem responding to the downstream O2 sensor. In particular, a slow response of the sensor is detected, which indicates that it takes more time than expected to move between rich and poor conditions. Various factors that affect how the sensors are able to provide accurate readings may be responsible for this discrepancy.


  • Defective Oxygen Sensor: One of the main root causes of the P0159 code is a deficient downstream O2 sensor. Slow reaction times can be caused over time by polluted or worn-out sensors.
  • Problems with the wire or connections: Corroded or damaged wiring and connectors connected to the downstream O2 sensor might obstruct the signal’s path and impair the sensor’s responsiveness.
  • Exhaust System Leaks: Any leaks in the exhaust system close to the O2 sensor’s downstream location might inject misleading air into the system and affect the sensor’s response.


  • Check Engine Light Illumination: The Check Engine Light illumination on the dashboard of the car is the P0159 code’s most obvious symptom.
  • Lower Fuel Efficiency: Inadequate fuel mixture management caused by a downstream O2 sensor that is faulty and has a poor reaction time might result in lower fuel economy.
  • Problems with engine performance: Due to inaccurate sensor readings, your engine may have less power, a rough idle, or trouble starting.


The P0159 code has to be diagnosed using a methodical process:

  • OBD-II Scanner: A skilled mechanic will access the vehicle’s Engine Control Module (ECM) with an OBD-II scanner to extract the recorded DTCs.
  • Visual Inspection: To check for any obvious damage or problems, the technician will visually examine the downstream O2 sensor, its wiring, and its connections.
  • Sensor Testing: To evaluate the downstream O2 sensor’s reaction time under varied exhaust circumstances, specialized diagnostic equipment may be employed.
  • Cross-checking: The technician can validate the problem by comparing the upstream O2 sensor readings and the actual sensor response time to the predicted values.

Common mistakes

  • As other factors such as electrical problems or exhaust system leaks may be contributing to the delay in response, it is necessary to replace the O2 sensor without identifying the root cause. 
  • Neglecting to look for related codes of trouble, which would add further information on the problem.

How serious is this?

There is no need to ignore the P0159 code, as it may not result in immediate and serious drivability problems. If an O2 downstream sensor fails and the response times are slow, there may be increased emissions and decreased fuel efficiency that can have more serious effects over time if not addressed.

What repairs can fix the code?

repair manuals

  • O2 Sensor Replacement: If the downstream O2 sensor is confirmed to be faulty or slow in response, replacing it with a new, high-quality sensor can resolve the issue.
  • Repairing wire or connections: Correct signal transmission and responsiveness can be restored by addressing any corroded, damaged, or attached wire and connections.
  • Repairing Exhaust System Leaks: The reaction time of the downstream O2 sensor can be enhanced by fixing any leaks in the exhaust system close by.

Related codes

  • P0147: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 3)
  • P0150: O2 Sensor Circuit (Bank 2, Sensor 1)


The P0159 DTC code shall relate to a downstream O2 sensor on Bank 2, which indicates an insufficient response from that sensor. The owners and mechanics of vehicles are empowered to take appropriate action when they understand the meaning, causes, symptoms, or possible remedies for this code. In order to maintain optimum engine performance, fuel efficiency, and emission control, timely diagnosis and resolution of the problem will be beneficial.

If you are confronted with the P0159 code and suspect your vehicle is experiencing problems related to O2 sensors, it is essential that you seek assistance from a qualified technician so as to be able to resolve these issues quickly and effectively.

P0159 Code – What Does It Mean & How To Fix It