Fault code P0156 – oxygen O2 sensor circuit malfunction (Bank 2, Sensor 2)

Fault code P0156 is called “Oxygen O2 Sensor Circuit Malfunction (Bank 2, Sensor 2)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0156

This Diagnostic Trouble Code (DTC) is a generic powertrain code. Error P0156 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly from model to model.

Fault code P0156 – oxygen O2 sensor circuit malfunction (Bank 2, Sensor 2)

Diagnostic code P0156 refers to the second oxygen sensor (O₂), located on Bank 2, after the catalytic converter. It measures the amount of oxygen entering the exhaust gases.

There are four wires coming to the O₂ sensor. Two wires are for the heating element and two wires are for the sensor data. The heater element must have battery voltage on one wire with the engine off. And ground on the other.

The PCM supplies 0.5 volt voltage to the O₂ sensor, which it varies depending on the oxygen content of the exhaust. The PCM also provides the grounding of the sensor.

Changes in the oxygen content, cause the resistance of the O₂ sensor to change. This change in resistance affects the 0.5 volt voltage supplied by the PCM. It can range from 0.1 to 0.9 volts. A value of 0.1 indicates complete depletion and 0.9 indicates complete enrichment.

The meaning of this code is that the O₂ (oxygen sensor) voltage has been low for more than 2 minutes, or the sensor is not active at all. This is perceived by the engine control module (ECM) as a malfunction and consequently error code P0156 OBD2 is set.

Symptoms of vehicle malfunctions

The main signal that an error P0156 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine indicator light on the control panel is on.
  2. Increased fuel consumption.
  3. Excessive smoke from the exhaust pipe.

Fault P0156 is not considered to be a serious fault, but when it does occur, it may increase fuel consumption, as well as excessive emission of harmful substances. Therefore, it is recommended to remove this fault as soon as possible.

Factors that can cause this error code

The error code P0156 can mean that one or more of the following problems have occurred:

  • The oxygen sensor O₂ may be defective.
  • There may be a voltage short circuit in the oxygen sensor signal circuit O₂.
  • High resistance or a break in the oxygen sensor signal circuit O₂.
  • Contact of wires with hot parts of exhaust system.
  • Damage and air leakage in front of the oxygen sensor.

How to fix or reset OBD-2 code P0156

Some suggested steps for troubleshooting and fix the error code P0156:

  1. Replace the faulty sensor.
  2. Eliminate short circuit, open circuit or high resistance in signal circuit O₂.
  3. Eliminate air leakage.

Diagnose and repair of problems

It is necessary to read out all saved data and error codes with an OBD-II scanner. Clear the error codes from the computer memory and test-drive the vehicle. To find out if code P0156 appears again.

To check the oxygen sensor voltage in real time using a scan tool. To find out if the sensor is working properly. Inspect the oxygen sensor electrical wires and connector for corrosion and damage.

Inspect the oxygen sensor for fluid contamination and damage. Test the exhaust system for exhaust gas leaks, and repair any leaks present, if necessary.

On which vehicles does this problem occur most frequently

Fault code P0156 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (A6)
  • BMW
  • Chevrolet (Avalanche, Silverado, Trucks)
  • Ford (F-150, Focus, Mondeo, Mustang, Taurus)
  • GMC (Truck)
  • Hyundai
  • Jeep
  • Kia
  • Lexus
  • Mercedes-Benz
  • Mitsubishi (Galant, Grandis, Pajero)
  • Subaru
  • Toyota (Avensis, Camry, Land Cruiser)
  • Volkswagen (Passat)

Fault code P0156 can sometimes be found with other errors. The most common are the following: P0051, P0056, P0133, P0136, P0157, P0171, P0303, P0411, P1131, P1151, P2197.


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