P0156 – Meaning, Causes, Symptoms, & Fixes

Code P0156 Definition

Oxygen Sensor Circuit Malfunction (Bank 2, Sensor 2)

What Does P0156 Mean?

Your car has O2 sensors that measure the amount of oxygen present in your exhaust. Based on the measures calculated, the O2 sensor will fluctuate between a high and low voltage. Your Power Control Module (PCM) uses the voltage levels provided by your O2 sensors to regulate your engine’s fuel injector pulse. When code P0156 is triggered, it means that your O2 sensor has remained at a low voltage for a prolonged period of time, which could be affecting your fuel levels.

Code P0156 Symptoms*

  • Check Engine Light
  • Decrease in MPG
  • Increased tailpipe emissions

*No noticeable adverse conditions in some cases

Code P0156 Causes

  • Wiring Problems
  • Leaks in the exhaust
  • Shorted voltage wires or circuits
  • Faulty fuel injectors

Code P0156 Severity – Moderate   

Generally, this code is not terribly serious. Your vehicle might experience an increase in fuel consumption, which is bad for you as a consumer who must purchase fuel. The increase in tailpipe emissions also means your vehicle is emitting pollutants into the air that are bad for the environment.

Code P0156 Common Diagnosis Mistakes

The most common mistake made when diagnosing code P0156 is replacing the O2 sensor immediately without visually inspecting any other relevant components of the vehicle. These include the fuel injectors, the wiring, and the exhaust.

P0156 Diagnosis

  • Tools Needed to Diagnose:

Difficulty of Diagnosis and Repair – (1-4)

  1. A sensor is needed for this next action, and the FIXD Sensor is perfect for it. Observe the live data from the O2 sensor and the fuel injector to see if they are both operating correctly.
  2. Note if the O2 sensor is rapidly or slowly switching from low to high voltage. This could indicate a faulty O2 sensor.
  3. Check for any broken or shorted wiring in relation to the O2 sensor. If there is any broken or shorted wiring, make sure to repair or replace it.
  4. Check for any vacuum leaks in the engine or any holes in the exhaust that could lead to air escaping from the engine. Repair any leaks or holes you find.
  5. If the issue is that either the O2 sensor or the fuel injector is faulty, your vehicle will need it to be replaced in order to run as efficiently as possible.

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Comments 2

Bulama Shettima

May 15, 2019


Steve Veltman

August 2, 2019

Neat little device

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