P0043 Fault Code

P0043 OBD-II Trouble Code Short Description

HO2S Heater Control Circuit Low (Bank 1 Sensor 3)

What does trouble code P0043 mean?

The P0043 fault code indicates a problem in the HO2S (heated oxygen sensor) heater control circuit for Bank 1 Sensor 3. The purpose of the HO2S is to measure the oxygen levels in the exhaust gases and provide feedback to the engine control module (ECM) for accurate fuel delivery.

The heater control circuit is responsible for heating the HO2S to its operating temperature quickly. This helps the sensor to reach its optimal working condition faster and provide accurate readings. A low voltage reading in the heater control circuit indicates that the circuit is not providing enough power to heat the sensor.

The possible causes of the P0043 code can include a faulty HO2S, a wiring issue in the heater control circuit, or a problem with the ECM.

To diagnose and repair this issue, you should start by inspecting the wiring and connections related to the Bank 1 Sensor 3 HO2S heater control circuit. Look for any signs of damage, loose connections, or corrosion. If any issues are found, repair or replace the affected wiring or connectors.

If the wiring appears to be in good condition, you can test the resistance of the HO2S heater element using a multimeter. A high resistance reading indicates a faulty sensor that needs to be replaced.

It is also recommended to check for any software updates for the ECM, as a programming issue can sometimes cause this fault code.

Once the issue is resolved, clear the fault code using a diagnostic tool. If the code returns, further diagnosis may be required to identify other potential causes.

Overall, fixing the P0043 fault code involves inspecting and repairing the wiring, replacing the faulty HO2S if necessary, and updating the ECM software if applicable.


What are the symptoms of the P0043 code?

  • Check Engine Light illuminated
  • Poor engine performance
  • Decreased fuel efficiency
  • Rough idle
  • Stalling or hesitation while accelerating
  • Failed emissions test


What causes the P0043 code?

The P0043 fault code usually occurs when the HO2S (Heated Oxygen Sensor) heater control circuit on Bank 1 Sensor 3 is detected to have low voltage. Some common causes of this fault code include:

  1. Faulty HO2S heater element: The heating element inside the oxygen sensor may become damaged or worn out, causing low voltage and triggering the fault code.

  2. Wiring issues: Problems with the wiring harness, connectors, or terminals associated with the HO2S heater circuit can prevent proper voltage delivery, resulting in the fault code.

  3. Blown fuse: A blown fuse in the heater circuit can disrupt the voltage supply to the HO2S, causing the fault code to appear.

  4. ECM (Engine Control Module) failure: In some rare cases, a malfunctioning ECM may incorrectly detect low voltage on the HO2S heater circuit, leading to the fault code.

It is recommended to thoroughly inspect the oxygen sensor, check the wiring connections, and test the heater circuit for voltage to diagnose and resolve the P0043 fault code. If necessary, consult a professional mechanic for further assistance.

Possible Solutions

How to fix P0043?

To fix the P0043 fault code on cars, you can follow these steps:

  1. Inspect the wiring: Check for any damaged or loose connections in the wiring harness associated with Bank 1 Sensor 3. Repair or replace any faulty wiring.

  2. Test the oxygen sensor: Using a multimeter, check the resistance of the oxygen sensor heater circuit. A resistance value lower than the specified range indicates a problem. Replace the oxygen sensor if needed.

  3. Inspect the fuse: Locate the fuse related to the oxygen sensor heater circuit and check if it is blown. If the fuse is blown, replace it with a new one of the same rating.

  4. Check the relay: Test the relay responsible for controlling the oxygen sensor heater circuit. Replace the relay if it is found to be faulty.

  5. Inspect the ECM: If all the above steps do not resolve the issue, there may be a problem with the Engine Control Module (ECM). Consult a professional technician to diagnose and repair any ECM-related issues.

Note: It is recommended to refer to the specific vehicle's repair manual for detailed instructions and specifications as the steps may vary depending on the make and model of the car.