What causes fault code P0043?

• Most likely: Faulty heater element inside the Oxygen Sensor (internal short or open) • Likely: Wiring harness damaged (rubbing against exhaust) causing a short to ground • Possible: Corroded or loose pins in the sensor connector • Rare: Internal failure in the Engine Control Module (ECM) heater driver circuit

How do you fix fault code P0043?

STEP 1: Visually inspect the connector for sensor 3 (post-catalytic) for moisture or corrosion. Check the wiring harness for heat damage or fraying against the exhaust pipe. STEP 2: Measure the resistance of the sensor's heater element using a multimeter (Ohm). Normal values are typically between 5 and 20 Ohms. Infinite resistance indicates an open circuit. STEP 3: Check for power supply. With ignition ON, there should be 12V at the heater supply pin. Verify the ground side control from the ECM using an oscilloscope (looking for PWM signal). STEP 4: If power and wiring are intact but sensor resistance is out of spec, replace the Oxygen Sensor. Clear codes and perform a drive cycle.

Powertrain (Engine & Gearbox)Standard EOBD

P0043 - HO2S Heater Control Circuit Low (Bank 1, Sensor 3)

Q: What are the symptoms of fault code P0043?

• Check Engine Light (MIL) illuminated • Vehicle may drive normally but emissions are increased • Slight decrease in fuel economy (as ECM may stay in Open Loop longer) • Failed emissions test

Last updated:1 February 2026

Related:O2-sensor (Bank 1, Sensor 3), Engine Control Module (ECM), Heater Circuit Fuse, Wiring Harness

System

Powertrain (Engine & Gearbox)

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P0000

No Diagnostic Trouble Codes (DTC) Present

P0001

Fuel Volume Regulator Control Circuit / Open

P0002

Fuel Volume Regulator Control Circuit Range/Performance

P0003

Fuel Volume Regulator Control Circuit Low

Technical Description

P0043 is set when the Engine Control Module (ECM) detects a low voltage condition in the heater control circuit of Oxygen Sensor 3, Bank 1. This sensor is the downstream sensor used primarily for monitoring catalytic converter efficiency. The HE heater element is critical for the sensor to reach its operating temperature of approximately 315°C (600°F). The ECM monitors the heater circuit via a dedicated driver; if the voltage remains low when the heater is commanded ON (indicating a potential short to ground or low resistance), this DTC is triggered. This typically involves PWM (Pulse Width Modulation) control to manage the heater's duty cycle.

Possible Causes

Faulty heater element inside the Oxygen Sensor (internal short or open)

Wiring harness damaged (rubbing against exhaust) causing a short to ground

Corroded or loose pins in the sensor connector

Internal failure in the Engine Control Module (ECM) heater driver circuit

Symptoms

Check Engine Light (MIL) illuminated

Vehicle may drive normally but emissions are increased

Slight decrease in fuel economy (as ECM may stay in Open Loop longer)

Failed emissions test

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P0043 - HO2S Heater Control Circuit Low (Bank 1, Sensor 3)

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P0043 - HO2S Heater Control Circuit Low (Bank 1, Sensor 3)

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