Engine and gearbox (P)
P0042: HO2S Heater Control Circuit Fault
This code indicates a problem with the heater control circuit for the oxygen sensor located on bank 1, sensor 3. This sensor is typically found downstream of the catalytic converter.
Checked by a licensed car technician · last reviewed 30 September 2026
Symptoms
- Check engine light on
- Increased emissions
- Poor fuel economy
Common causes
- Heater element open
- Faulty wiring or connector
- Blown fuse
- Faulty oxygen sensor
- Faulty engine control module (ECM)
How to check it yourself
- Inspect and test the fuse related to the oxygen sensor heater
- Check wiring and connectors for damage or corrosion
- Test the heater element for continuity
- Inspect the oxygen sensor for damage
- Check the ECM for faults
Can I keep driving?
The car can still be driven, but it may have increased emissions and reduced fuel efficiency.
General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer