Diagnosing P0135 Code: O2 Sensor Heater Circuit Malfunction Explained

Diagnosing P0135 Code: O2 Sensor Heater Circuit Malfunction Explained

If you’ve ever seen your check engine light illuminate and had your vehicle scanned, you may have encountered the P0135 trouble code. This diagnostic code is more common than you might think and can affect a wide range of vehicles. In this blog post, we’ll dive deep into what the P0135 code means, which vehicles are commonly affected, and how to address this issue.

What is the P0135 Code?

The P0135 code indicates an “O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1).” This means that the engine control module (ECM) has detected a problem with the oxygen sensor heater circuit in the first O2 sensor of bank 1. The oxygen sensor plays a crucial role in monitoring the exhaust gases and helping the ECM adjust the air-fuel mixture for optimal engine performance and emissions control.

Top 20 Vehicles Commonly Affected by P0135 Code

While the P0135 code can appear in various makes and models, here are some vehicles where this code is frequently encountered:

  1. Toyota Camry
  2. Honda Accord
  3. Ford F-150
  4. Chevrolet Silverado
  5. Nissan Altima
  6. Honda Civic
  7. Toyota Corolla
  8. Ford Focus
  9. Hyundai Elantra
  10. Chevrolet Cruze
  11. Volkswagen Jetta
  12. Mazda3
  13. Subaru Outback
  14. Kia Optima
  15. BMW 3 Series
  16. Audi A4
  17. Mercedes-Benz C-Class
  18. Lexus RX
  19. Jeep Grand Cherokee
  20. Ram 1500

Implications for Vehicle Performance and Emissions

The P0135 code can have several implications for your vehicle:

  • Reduced Fuel Efficiency: Incorrect air-fuel mixture adjustments can lead to increased fuel consumption.
  • Rough Idling or Poor Engine Performance: The engine may run poorly or have difficulty idling smoothly.
  • Failed Emissions Test: The vehicle may not pass emissions tests due to incorrect sensor readings.
  • Increased Exhaust Emissions: Higher emissions due to improper air-fuel mixture.
  • Possible Engine Stalling: The engine may stall or run inadequately.

Diagnosing and Fixing the P0135 Code

Here’s a comprehensive guide to diagnosing and addressing the P0135 code:

  1. Use an OBD-II Scanner: Confirm the P0135 code and check for any additional codes.
  2. Visual Inspection:
    • Check the oxygen sensor’s electrical connections, wire harness, and metal tabs for damage.
    • Inspect for exhaust leaks or vacuum leaks that could affect sensor readings.
  3. Test the O2 Sensor Heater Circuit:
    • Use a multimeter to check the resistance of the heater circuit.
    • Verify the voltage supply to the O2 sensor.
  4. Check the Fuse and Relay: Ensure the fuse and relay for the O2 sensor heater circuit are functioning correctly.
  5. Inspect Wiring: Look for any damaged, corroded, or loose wiring in the O2 sensor circuit.
  6. Replace the O2 Sensor: If all other checks pass, the O2 sensor itself may be faulty and require replacement.

Key Symptoms and Solutions


  • Illuminated check engine light
  • Reduced fuel efficiency
  • Rough idling or poor engine performance
  • Failed emissions test


  • Replace faulty O2 sensor
  • Repair damaged wiring or connectors
  • Fix exhaust or vacuum leaks
  • In rare cases, replace ECM/PCM

FAQ Section

Q: Is it safe to drive with a P0135 code? A: While you can drive short distances, it’s not recommended for long-term driving as it can lead to reduced fuel efficiency and potential engine damage.

Q: What are the potential repair costs for a P0135 code? A: Costs can vary depending on the underlying issue. O2 sensor replacement typically ranges from $200 to $500, including parts and labor.

Q: How can I prevent the P0135 code from appearing in the future? A: Regular maintenance, including timely replacement of worn O2 sensors and addressing exhaust leaks promptly, can help prevent this issue.

Q: How long does it take to fix a P0135 code? A: The repair time can vary, but typically it takes 1-2 hours for a professional mechanic to diagnose and fix the issue.


The P0135 trouble code, while common, should not be ignored. Addressing this issue promptly can help maintain your vehicle’s performance, fuel efficiency, and compliance with emission standards. If you’re not comfortable performing the diagnostics or repairs yourself, don’t hesitate to consult a professional mechanic. Remember, keeping your vehicle in top shape not only ensures a smoother ride but also contributes to a cleaner environment.

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