O2 Sensor Heater Control Circuit Malfunction (Bank 1 Sensor 3)
The P0042 code indicates a problem with the heater control circuit for the oxygen sensor located after the catalytic converter on bank 1 (engine side with cylinder #1). The heater element inside the sensor helps it reach operating temperature quickly. When the Powertrain Control Module (PCM) detects an open, short, or excessive resistance in the heater circuit, it sets this code. This can lead to inaccurate air-fuel ratio readings, increased emissions, and potential catalytic converter damage.
01. Most Common Causes
- Faulty oxygen sensor (Bank 1 Sensor 3)
- Blown heater circuit fuse
- Open or shorted wiring in the heater circuit
- Corroded or damaged connector
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Failed emissions test
- Decreased fuel economy
- Rough idle or hesitation
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 wiring and connector for Bank 1 Sensor 3 for damage, corrosion, or loose connections.
Step 3: Check the heater circuit fuse and replace if blown.
Step 4: Measure resistance across the heater terminals of the sensor; compare to manufacturer specs (typically 5-30 ohms).
Step 5: If resistance is out of range, replace the oxygen sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause poor fuel economy and increased emissions. Prolonged driving could damage the catalytic converter.
How much does it cost to fix?▼
Typically $50-$150 for a DIY sensor replacement, or $150-$300 at a shop including labor.