P0135 – O2 Sensor Heater Circuit

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The oxygen sensors in your car help the engine control unit regulate everything from the amount of fuel injected into the engine to the exhaust quality. It might seem like a relatively small and unimportant component, but it can lead to severe problems down the line if your oxygen sensor fails.

The P0135 OBD2 code is triggered when an issue is detected in your oxygen sensor’s heat circuit. This doesn’t always mean the sensor itself has failed, however. The wires, fuses, and other components connected to the sensor are sometimes the bad readings’ root causes.

In most situations, the solution to the P0135 code is a simple fix. Read on to learn what steps you should follow when it’s time to diagnose it.

P0135 Code Definition

  • P0135 Code Definition (Generic): Oxygen O2 sensor heater circuit malfunction (bank 1, sensor 1)
  • P0135 Chevy Code Definition: H02S heater performance bank 1 sensor 1
  • P0135 Honda Accord Code Definition: O2 sensor heater circuit malfunction bank 1 sensor 1
  • P0135 Honda Civic Code Definition: O2 sensor heater circuit malfunction bank 1 sensor 1
  • P0135 Jeep Code Definition: O2 sensor heater circuit malfunction bank 1 sensor 1
  • P0135 Nissan Code Definition: H02S11 heater circuit fault
Here's where you can get a thorough understanding of the P0135 OBD2 code
If you want to learn about the P0135 OBD2 code, this is the right place

What Does P0135 Mean?

Modern engines use heated oxygen sensors that are designed to get to temperature quickly. The heating elements inside these sensors help minimize the amount of time the system is in an open loop with a fixed rich mixture.

When the heater in the sensor reaches operating temperature, the oxygen sensor begins to respond to the air’s oxygen content around it. If it takes too long for this operation to kick in, the P0135 trouble code will trigger. It specifically points you toward oxygen sensor 1 on bank 1.

The powertrain control module tests the heaters inside the oxygen sensors periodically to ensure they’re operating correctly. If these tests detect either a short circuit or too much resistance, this will also trigger the P0135 trouble code.

What Are The Symptoms of The P0135 Code?

The symptoms of this trouble code are relatively mild. In fact, you may not notice any drivability issues. The typical signs you’ll see from your car are:

  • Activation of the check engine light
  • Reduced fuel economy
  • Engine runs rough, especially while heating up
P0135 code related to O2 sensor Heater Circuit.
P0135 code tells you that you have to check the O2 sensor Heater Circuit.

What Are The Causes of P0135?

  • Faulty oxygen sensor
  • Faulty engine coolant temperature sensor
  • Faulty wiring or connections around the oxygen sensor
  • Wiring has shorts or open grounds
  • Faulty power control module
  • Vacuum leak before the oxygen sensor
  • Faulty catalytic converter

How Serious Is The P0135 Code?

The P0135 trouble code isn’t serious by itself. However, if left unresolved, it could lead to issues that are serious and costly. It would be best to make repairs as soon as possible when you notice this code has activated.

How To Diagnose The P0135 Code

Tools you’ll need


  1. Inspect the wires around the oxygen sensor to make sure none of them are frayed or damaged. Also, check the connections and make sure they’re all secure.
  2. Read the freeze frame data using an OBD2 scan tool to check what conditions were present when the code was triggered.
  3. Monitor your oxygen sensor data. This should tell you if the heater circuit is working properly.
  4. Check the wire harness around the oxygen sensor for moisture. If water gets into the harness, it can cause shorts and corrosion.
  5. Use a digital multimeter to make sure the oxygen sensor is reading a voltage. Before you test it, disconnect the harness and turn the ignition on without starting the engine.
  6. Look for damage on the metal tabs, terminals, and connections around the oxygen sensors.
  7. Inspect the vacuum tubes on your exhaust system for leaks. Make sure to also feel along the undersides for hidden weak spots and cracks. Pay special attention to the ends of hoses, which can leak or fray.
  8. Find and inspect your engine ground. Make sure the connection is tight. Also, check for corrosion, as you may need to clean or replace the ground.
  9. Use a vacuum gauge to test your catalytic converter. With the engine at operating temperature, the reading should be between 18 and 22 in-Hg. When you rev the engine, the vacuum readings should drop slightly then return to that level. If they don’t, your exhaust system is likely blocked. Remove and clean your catalytic converter.

Common Mistakes to Avoid While Diagnosing The P0135 Code

Don’t assume P0135 means you have a problem with your sensor just because it’s named in the diagnostic code. The problem could be a system’s mechanical issue, such as a fault wire or a leak in your exhaust. Make sure you conduct a full diagnosis before you replace any components.

What Should You Do to Fix The Code P0135?

  1. Replace any damaged wires, connectors, or circuits found during your diagnosis.
  2. Clear the codes using an OBD2 scan tool. Conduct a road test, ensuring your vehicle has sufficient time to reach operating temperature. The simple repairs made during your diagnosis may clear the code. If it doesn’t, continue with step 2.
  3. Replace the fuse to the heater circuit. The fuse often blows if the code was triggered by a short in your system.
  4. Remove and clean your oxygen sensor using a mass air flow sensor cleaner. Also, check and clean the connectors around the sensors.
  5. Clear the codes and test drive your car again. If the P0135 OBD2 recurs, replace your oxygen sensor.
  6. If the code still doesn’t clear, you may have a more serious issue with your electrical system. Take your car to a mechanic for further diagnosis.
P0135 Code Oxygen sensor on 2002 Honda Accord.

Tips To Avoid P0135 In The Future

Short circuits and damaged wires are some of the most common causes of the P0135 trouble code. Preventing them is the best way to avoid it. Make sure none of the wires in your engine are in contact with anything that could damage them, including sources of high heat. Check that none of the wires are overlapping with each other so that it can lead to short circuits as well.

You can also generally prevent damage to your engine’s components by treating it with a rust-preventing spray. This will help to minimize corrosion throughout your engine.

Read More: P0420: Meaning, Symptoms, Causes, Diagnostics, and Fixes