DTC P0043 HO2S Heater Control Circuit Low Bank 1 Sensor 3

DTC P0043 is a diagnostic trouble code indicating an issue with the heater control circuit of the oxygen sensor located at Bank 1 Sensor 3. Understanding and addressing this issue is crucial for maintaining your vehicle’s efficiency and performance. In this article, we’ll delve into the details of DTC P0043, exploring what it means, its potential causes, and how to diagnose and fix this issue effectively.

What is DTC P0043?

The P0043 diagnostic trouble code (DTC) signifies that there is a low voltage condition in the heater control circuit of the heated oxygen sensor (HO2S) located on Bank 1, Sensor 3. The heater element in an oxygen sensor helps it reach its operating temperature quickly, ensuring accurate readings of the oxygen levels in the exhaust gases. When the ECM (Engine Control Module) detects an issue with the heater circuit, such as low voltage, it sets the P0043 code. This problem can lead to delayed sensor response, affecting the engine’s air-fuel mixture adjustments, resulting in decreased performance and fuel efficiency.

Potential Causes of DTC P0043:

The P0043 code is triggered when the ECM detects a low voltage condition in the heater control circuit of the oxygen sensor. This can happen due to several reasons:

  • Faulty Oxygen Sensor: The most common cause is a defective oxygen sensor heater element.
  • Wiring Issues: Damaged, corroded, or broken wires in the heater circuit can cause this code.
  • Blown Fuse: A fuse related to the oxygen sensor heater circuit might be blown.
  • Faulty ECM: Although rare, a malfunctioning ECM could incorrectly manage the heater control circuit.
  • Relay Issues: Problems with the relay controlling the heater circuit can also trigger this code.

Symptoms of P0043

When the P0043 code is set, you might experience the following symptoms:

  • Check Engine Light (CEL) illuminated on the dashboard.
  • Increased fuel consumption.
  • Possible rough idling or poor engine performance due to delayed sensor response.
  • Emissions test failure due to improper air-fuel mixture adjustments.

Diagnostic and Repair Procedures for DTC P0043:

Diagnosing and resolving the P0043 code requires a systematic approach:

  1. Initial Inspection: Connect a diagnostic scanner to the vehicle’s OBD-II port to retrieve the trouble codes, including P0043. Record any additional codes and freeze frame data to understand the conditions under which the code was set.
  2. Visual Inspection: Conduct a thorough visual inspection of the oxygen sensor and its wiring harness. Look for signs of damage, corrosion, or disconnections.
  3. Check Fuse and Relay: Inspect the fuse and relay associated with the oxygen sensor heater circuit. Replace any blown fuses or faulty relays.
  4. Test Oxygen Sensor Heater Circuit: Use a multimeter to measure the resistance of the heater element in the oxygen sensor. Compare the readings with the manufacturer’s specifications. Replace the sensor if the heater element is faulty.
  5. Inspect Wiring and Connections: Perform a continuity test on the wiring harness associated with the oxygen sensor heater circuit. Ensure there are no breaks, shorts, or crossed wires. Repair or replace any damaged wiring as necessary.
  6. Check for ECM Issues: Although rare, inspect the ECM for any potential faults or software issues that could cause incorrect management of the heater control circuit. Reprogram or replace the ECM if necessary.
  7. Clear Codes and Perform Test Drive: After completing the repairs, clear the trouble codes from the vehicle’s memory using the diagnostic scanner. Perform a test drive to ensure the vehicle operates properly and that the P0043 code does not return.


Understanding and addressing DTC P0043 is essential for maintaining optimal engine performance and fuel efficiency. By following these detailed diagnostic and repair procedures, you can effectively address the P0043 trouble code, ensuring the vehicle’s oxygen sensor heater circuit functions correctly. Regular maintenance and careful inspection of wiring and connections can help prevent this code from appearing. If you found this guide helpful, please share it with fellow automotive enthusiasts and technicians. For more detailed guides and tips on car maintenance and repair, visit our website.