P0135 — O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
The heating element inside the upstream oxygen sensor draws no current, draws too much current, or is open-circuit. The heater brings the sensor to operating temperature so closed-loop control can start within seconds rather than minutes.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Oxygen sensor upstream
- Oxygen sensor heater relay
- Oxygen sensor heater fuse
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Heater element open-circuit
- Heater fuse blown
- Wiring fault to heater
Possible symptoms
- Check engine light on after several drive cycles
- Slightly increased fuel consumption during cold start
- Delayed entry into closed-loop fuel control
- Failed emissions inspection (lambda readiness)
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.