P0042 Fault Code

P0042 OBD-II Trouble Code Short Description

HO2S Heater Control Circuit (Bank 1 Sensor 3)

What does trouble code P0042 mean?

The P0042 fault code refers to a problem with the HO2S (Heated Oxygen Sensor) Heater Control Circuit of Bank 1 Sensor 3. The Bank 1 Sensor 3 is the third oxygen sensor in the exhaust system of the engine, located on the side of the engine bank that contains cylinder 1.

The HO2S is responsible for measuring the oxygen content in the exhaust gases and providing feedback to the engine control module (ECM) for proper fuel delivery and emissions control. The heater control circuit in the oxygen sensor ensures that it reaches operating temperature quickly and maintains it during operation.

When the P0042 code is triggered, it means that the ECM has detected a malfunction in the heater control circuit of the Bank 1 Sensor 3 oxygen sensor. This can be caused by various issues, such as a faulty sensor, a damaged wiring harness, or a problem with the ECM itself.

The solution to this problem involves several steps:

  1. Inspecting the oxygen sensor wiring: Check for any damaged wires, loose connections, or corrosion in the wiring harness. Repair or replace as necessary.

  2. Testing the oxygen sensor: Use a multimeter to measure the resistance of the heater circuit in the oxygen sensor. If the resistance is outside the specified range, the sensor may need to be replaced.

  3. Checking the ECM: Perform a thorough diagnostic scan of the ECM to check for any related fault codes or issues. If other codes are present, they need to be addressed first before focusing on the P0042 code.

  4. Clearing the fault code: After any repairs or replacements, clear the fault code using an OBD-II scanner. This will reset the ECM and allow it to re-evaluate the sensor's performance.

It is important to address the P0042 code promptly as it can negatively affect fuel efficiency, emissions, and overall engine performance. If you are not confident in diagnosing and repairing the issue yourself, it is recommended to seek assistance from a qualified mechanic or automotive technician. They will have the necessary tools and expertise to properly diagnose and resolve the problem.


What are the symptoms of the P0042 code?

  • Check Engine Light is illuminated
  • Poor engine performance
  • Decreased fuel efficiency
  • Rough idle
  • Increased emissions
  • Possible heater element failure in Bank 1 Sensor 3 oxygen sensor.


What causes the P0042 code?

The P0042 fault code refers to the HO2S (Heated Oxygen Sensor) heater control circuit for Bank 1 Sensor 3. This fault code is typically found in vehicles with multiple oxygen sensors.

Possible causes of the P0042 fault code include:

  1. Faulty heated oxygen sensor (Bank 1 Sensor 3): The oxygen sensor may be damaged or worn out, preventing it from properly measuring the oxygen levels in the exhaust gases.

  2. Open or short in the heater control circuit: There may be a wiring issue, such as a broken or frayed wire, or a loose connection in the heater control circuit for the oxygen sensor.

  3. Faulty heater control circuit relay: The relay that controls the heater circuit for the oxygen sensor may be malfunctioning, preventing the sensor from getting the required voltage.

  4. Faulty engine control module (ECM): The ECM may be sending incorrect signals or not providing power to the oxygen sensor heater circuit, resulting in the fault code.

It is recommended to perform a thorough inspection of the oxygen sensor, wiring, and electrical connections. If any faults are found, repairs or replacements should be carried out accordingly to resolve the P0042 fault code.

Possible Solutions

How to fix P0042?

To fix the P0042 fault code on cars, follow these steps:

  1. Check the wiring: Inspect the wiring harness and connectors connected to the Bank 1 Sensor 3 oxygen sensor (HO2S). Look for any signs of damage or loose connections. If any issues are found, repair or replace the wiring as necessary.

  2. Test the oxygen sensor: Use a multimeter to check the resistance of the Bank 1 Sensor 3 oxygen sensor's heater circuit. The resistance should typically be around 4-10 ohms. If the resistance is out of range, the oxygen sensor may need to be replaced.

  3. Replace the oxygen sensor: If the wiring and resistance tests are all okay, it is possible that the Bank 1 Sensor 3 oxygen sensor has failed and needs to be replaced. Remove the old sensor and install a new one.

  4. Clear the fault code: After performing the necessary repairs or replacements, use an OBD-II scanner to clear the fault code from the car's computer. This will reset the system and allow you to monitor if the fault code reoccurs.

Please note that these steps are general guidelines, and it is always recommended to consult the specific vehicle's repair manual or seek professional assistance for accurate diagnosis and repair.