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  • DTC P0042 stands for “HO2S Heater Control Circuit Bank 1 Sensor 3”
  • This code is logged when the PCM detects a problem with the heater circuit of the third sensor downstream from the engine on bank 1.
  • Code P0042 is commonly caused by a faulty oxygen sensor or problems with the oxygen sensor heater control circuit.
  • Other DTCs may be logged together with this code. It is similar to codes P0043 and P0044.

If you’re having trouble figuring out what code P0042 means and how to resolve it, you’ve come to the right place. Read on to learn more about P0042, its triggers, and common symptoms you should look out for.

What Does the P0042 Code Mean?

Diagnostic trouble code (DTC) P0042 stands for “HO2S Heater Control Circuit Bank 1 Sensor 3.” It is logged when the powertrain control module (PCM) detects a possible issue with the heater circuit for the third sensor downstream from the engine on bank 1.

When there are only 3 O2 sensors it’s typically because there’s only one catalyst being monitored, and “Bank 1” is the default designation when there’s only one sensor in a category.

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oxygen sensor diagram
Diagram showing 3 oxygen sensors | Image Source: Richard McCuistian

Bank 1 is the side of the engine where the #1 cylinder is located. P0042 code is set when your car’s PCM determines a potential problem with the heater element circuit of the oxygen sensor.

Newer car models determine oxygen content through heated oxygen sensors in the exhaust system before and after the catalytic converter(s). The information supplied by the oxygen sensors helps the fuel system maintain the right air to fuel ratio. Downstream oxygen sensors also help the PCM determine the efficiency of the catalytic converter.

oxygen sensor lambda sensor in exhaust
The information supplied by the oxygen sensors helps the fuel system maintain the right air to fuel ratio.

The oxygen sensor is designed to measure the amount of oxygen present in the exhaust gasses exiting the engine. Remember, the O2 sensor doesn’t detect fuel, so a misfiring cylinder may initially show up as a lean condition due to the oxygen exiting the cylinder with the unburned fuel

For the information relayed by the oxygen sensor to be accurate, it has to be kept at a certain temperature. That’s where the oxygen sensor’s heater element comes in. When the PCM detects an issue with the heater wire inside the sensor, specifically in bank 1 sensor 3, code P0042 is set.

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Note: The definition of code P0042 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Possible Causes of the P0042 Code?

P0042 is a generic code, so it can have several triggers. Here are the most common:

mechanic repairing vehicle engine
To ensure your engine remains in top condition, code P0042 should be resolved immediately.

What are the Common Symptoms of the P0042 Code?

Depending on the severity, other related DTCs may also be stored. Code P0042 is very similar to error codes P0043 and P0044. Generally, you may notice this symptom if you drive a vehicle with a set P0042 trouble code:

How to Diagnose the P0042 Code

To ensure your engine remains in top condition, code P0042 should be resolved immediately. However, diagnosing this code can be tricky as it may have many potential causes. The diagnostic and repair steps should depend on the specifications of your vehicle. For instance, a P0042 on a Silverado may require a different diagnosis from a P0042 on a Forester.

Check out the video below to get an idea of what the diagnostic process might involve:

How to Fix the P0042 Code

Like other OBD-II codes, there is no fixed solution for a P0042 code. Although the P0042 engine code shares similar triggers and symptoms with various other trouble codes, it doesn’t have a universal solution.

See also  P0141 Code: Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

Repair and diagnostic steps still depend on the specifications of your vehicle, so consult a vehicle-specific repair manual before proceeding.

If you’re not well-versed in auto repair, it may be best to leave the job to a mechanic. Otherwise, you can do the repairs yourself. There are online auto repair sources you can use as a guide to help you identify which repair steps apply to your vehicle.

It may also be a good idea to subscribe to ALLDATA for detailed factory repair information. It can help you fix error code P0042 and serve as a reference for future trouble codes you may encounter.

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About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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