P0042 code definition

P0042 is telling us the ECM has detected a fault in the heated oxygen sensor control circuit for bank 1 sensor 3. This can be associated with P0043 and P0044

What the P0042 code means

The heated oxygen sensor’s heater circuit is controlled by the car's engine control unit (ECU). P0042 tells us there is an issue between the ECU and the oxygen sensor bank 3 sensor 1. This heating element is required for proper sensor readings.

What causes the P0042 code?

There are a few possible causes for P0042:

  • Bank 1 sensor 3 sensor failure
  • Open or shorted sensor wiring
  • Damaged wiring
  • Rarely ECU failure may be the cause

What are the symptoms of the P0042 code?

The first thing that will happen is the ECU will try to control the heater circuit for heated oxygen sensor bank 1 sensor 3. When the car’s ECU detects an issue with the control circuit it will trigger a Check Engine Light to show on the dash. This Check Engine Light may be flashing.

How does a mechanic diagnose the P0042 code?

There are a few steps for diagnosing P0042:

  • First, a qualified technician will hook up a scan tool to the car’s OBD-II port to confirm P0042 is present.

  • The technician will look for any freeze frame data with the code.

  • Next, the technician will clear the code.

  • After the code is cleared, the vehicle will be taken on a test drive under the same conditions. The freeze frame data tells us about the conditions from when the previous code was set at.

  • Once the code reappears, the technician will perform a visual inspection of the bank 1 sensor 3 and its associated wiring.

  • If the wiring is okay, the sensor itself will be tested to confirm operation.

  • After the oxygen sensor is tested and found to pass, the technician will perform any tests required to confirm proper operation of the ECU.

Common mistakes when diagnosing the P0042 code

The most common error is not performing all tests and steps to properly diagnose P0042. The sensor must be tested for proper operation before it is replaced.

How serious is the P0042 code?

P0042 is not a particularly serious code. The heater circuit of bank 1 sensor 3 is required for accurate readings and may cause improper readings and/or poor fuel economy until it is repaired.

What repairs can fix the P0042 code?

There are a few simple repairs that can fix P0042:

Additional comments for consideration regarding the P0042 code

P0042 can be an easy code to diagnose and repair as long as step-by-step diagnostic is performed and parts are not replaced before they are tested.

Need help with a P0042 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

This article originally appeared on YourMechanic.com as P0042 OBD-II Trouble Code: HO2S Heater Control Circuit (Bank 1 Sensor 3) and was authored by Spencer Clayton.


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