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P0042 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.


This code shows that there is a fault with the H02S heater control circuit for bank one sensor three. Modern vehicles use oxygen sensors that determine the concentration of oxygen that is in the exhaust.

When the bank one sensor three wiring fails, inaccurate signals will be sent to the engine control module. This will cause the check engine light to illuminate.


This diagnostic trouble code is a generic powertrain code, which means that it applies to OBD-II equipped vehicles, including but not limited to VW Volkswagen, Audi, Mazda, Ford, Chevy and more. While it is generic, the specific repair steps may vary depending on the make and model of the vehicle. Fuel injected vehicles use heated oxygen sensors in the exhaust system before and after the catalytic converters to determine oxygen content. This feedback is used to adjust the fuel system accordingly to maintain a proper air to fuel ratio of 14.7:1.


There are several causes of the P0042 DTC code including a failure of the bank one sensor one, sensor wiring that is open or shorted, wiring that is damaged or an ECU failure in rare cases. Another potential cause is the corrosion of the exhaust system ground strap. Failure of the wiring for the PCM, ECM or the oxygen sensor heater circuit could also cause P0042 DTC.


Symptoms of a P0042 DTC include malfunction indicator lamp illumination. You will probably not notice any other symptoms associated with the failure of the heated circuit since it only runs momentarily when the vehicle is first started. This sensor is also after the catalytic converter, so it will not affect the air to fuel ratio input to the PCM and ECM; it is primarily used to verify the catalytic converters efficiency.

The presence of the check engine light from P0042 DTC will cause you to fail emissions testing if it is required.


The first step that you should take when diagnosing any malfunction is to spend some time researching the Technical Service Bulletins to find any known issues with your vehicle. This can save you a significant amount of time if the symptoms match common issues.

There are specific steps that a mechanic will take in order to properly diagnose P0042 DTC. They will start by hooking up a scan tool to the OBD-II port to verify the presence of P0042. They will then look for any freeze frame data within the code and clear it. Once this code is cleared, a test drive will be performed. A visual inspection of bank one sensor three and the wiring will be performed once the code reappears. If the wiring is functioning properly, tests will be performed on the sensor. Once the oxygen sensor passes a test, the diagnosis will be finished by testing for the correction operation of the ECU.

The process of diagnosing P0042 DTC must be performed precisely in order to ensure accuracy. One mistake in the process can cause a misdiagnosis, which means that you will be performing the improper repairs. Hiring a professional mechanic to test your vehicle is the best way to test for OBD-II trouble codes.

Common mistakes

The most common mistake that people make when attempting to diagnose P0042 DTC is to not perform all of the necessary tests that are required for a proper diagnosis. The sensor itself must be tested before it can be replaced.

How serious is this?

P0042 DTC is not a serious code because it will not cause serious damage or problems for your vehicle. The bank one sensor three heater circuit must be operating properly in order to provide accurate reading. You may also experience poor fuel economy until the proper repairs are performed.

What repairs can fix the code?

repair manualsrepair manuals

There are a few repairs for P0042 DTC that are fairly easy to perform. You may need to replace the crankshaft sensor, signal plate, PCM or wiring harness. The engine timing belt or chain may also need to be fixed as well as any other mechanical damage.

Related codes

P0043 and P0044 codes are often associated with P0042 DTC.


P0042 DTC is a code that is both easy to diagnose and repair, and will not cause serious issues for your vehicle. A professional mechanic will follow all of the steps of the diagnostic process, and test all of the parts before replacing them.

P0042 Code – What Does It Mean & How To Fix It