O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 3)
The P0043 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the heater control circuit for the oxygen sensor located downstream of the catalytic converter on Bank 1 (the side of the engine containing cylinder #1). This sensor (Sensor 3) is typically the second rear oxygen sensor. The heater circuit is essential for the sensor to reach operating temperature quickly, especially during cold starts. A low voltage reading suggests a short to ground, open circuit, or a faulty sensor or PCM.
01. Most Common Causes
- Faulty oxygen sensor (Bank 1 Sensor 3)
- Blown fuse or open circuit in the heater power supply
- Short to ground in the heater control circuit wiring
- Corroded or damaged connector at the oxygen sensor
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Increased emissions
- Possible poor fuel economy
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the oxygen sensor connector and wiring for damage, corrosion, or loose connections.
Step 3: Test the heater circuit resistance at the sensor connector (typically 2-10 ohms). If out of range, replace the sensor.
Step 4: Check for battery voltage and ground at the heater circuit with the ignition on. If no voltage, check fuses and relays.
Step 5: If voltage and ground are present but the code persists, test the PCM output; if faulty, replace the PCM.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but the vehicle may fail an emissions test and fuel economy may suffer. It's best to repair it promptly to avoid catalytic converter damage.
How much does it cost to fix?▼
Typically $50-$150 for a DIY replacement of the oxygen sensor. Professional repair may cost $150-$300 including labor.