P0135 – O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

P0135 pops up on your scan tool screen and you don’t know whether it’s serious or not?

Now, let’s take a quick look at the information below.

  • Definition: Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
  • Code type: Generic – P0135 indicates the same problem whether you’re having a Honda, Chevy, or Ford, etc.    
  • Can I drive with the P0135 code? Yes, you can, but don’t because it will cause more damage to the engine parts. 
  • Easy to fix? DIY to advanced levels
  • Cost: $30-$150 (common)

To help you understand the P0135, I will discuss the code’s meaning, causes, symptoms, diagnosis, and solutions in this guide. 

So, keep reading to unveil more details. 


Table Of Contents


What Does The P0135 Code Mean?

P0135 stands for Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1). This code is set when the PCM detects an unsuitable heated oxygen sensor (HO2S) 1 heater current in a given time.

  • Bank 1: Refers to the engine side that contains cylinder 1
  • Sensor 1: It’s the upstream oxygen sensor, responsible for measuring the oxygen in the exhaust.

The O2 sensor 1 helps in controlling the air-fuel ratio. The PCM uses information from the O2 sensors to control emissions and regulate the fuel-air mixture. 

For the O2 sensors to convey accurate information, it must be hot enough. For that reason, it contains an integrated heater circuit which helps maintain the ideal operating temperature during the process. If the circuit malfunctions, it sets up the P0135 code.

Besides, the P0135 can pop up with other DTCs such as P0141, P0161, P0155, and P0300. 


P0135 Causes Identification: Quick View

The P0135 code can majorly result from having problems with the sensor itself. However, the error can result from other underlying issues. 

Check the table below to determine some common causes of P0135 and its related codes.

Codes combinationCauses Solutions
P0135 onlyFaulty oxygen sensor.
Short/open circuit in the wiring.
Faulty coolant temperature sensor.
Replace the oxygen sensor.
Fix the oxygen sensor’s wiring.
Replace the coolant temperature sensor.
P0135 + P0141/ P0161/P0155Blown fuseLocate the O2 sensor heater fuse and replace it.
P0135 + P0300Faulty PCM.Replace the PCM.

P0135: Causes, Symptoms, And How To Fix

Cause #1: Faulty Oxygen Sensor

The oxygen sensors are found at the exhaust manifold, where they control the entire combustion process. The sensors measure the amount of oxygen in the exhaust gasses. Further, it conveys the data to the PCM to determine if the engine is burning too much or too little fuel.

The PCM makes adjustments to ensure the air-fuel ratio is at its best for proper combustion. If the oxygen sensor malfunctions, it will interfere with the entire combustion process, thus setting up the P0135 code.

Faulty oxygen sensor symptoms:

  • Weak engine performance
  • Rough idling
  • Failed emission test

When you notice the oxygen sensor is bad, replace it immediately. The process is simple and can cost you a few dollars, depending on your vehicle model.

Replacing O2 sensor is quite simple and you can totally do it by yourself. Let’s find out how to do with the thorough instruction from Mr. Kilmer.

Cause #2: Blown Fuse

A fuse is a vital component that protects electrical circuits when there is a current overflow. For that reason, most vehicles utilize fuses in the oxygen sensor and air-fuel ratio heater circuits to prevent them from overcurrent flow.

The fuses blow to protect the O2 sensor circuit in case of current overflow. As a result, the process cuts the operation of the oxygen sensors, thus throwing the P0135 code. 

The most common symptom of a blown fuse is the engine hard start.

In this case, identify the blown fuse and replace it with a new one. The issue is not severe; hence there is no need for mechanical savvy.

Cause #3: Short/ Open Circuit In The Heater Wiring

The heater heats the sensor to its operating temperature so it can start working as soon as possible. 

In the case of a short/open circuit in the heater wiring, electricity is hindered from reaching the sensor. The PCM detects the issue and thus sets up the P0135 code. 

Symptoms of short/open circuit in the heater wiring:

  • Poor acceleration and engine performance
  • Engine hard start
  • The engine takes time to heat up after a cold start
  • Rough idling

In this scenario, you should fix the sensor wiring to do away with P0135. 

The process begins by measuring the wiring harness using a multimeter to verify the presence of an open/short circuit. The multimeter should read 12 volts. 

Otherwise, the wiring has a problem hence the need to fix it.

Testing O2 sensor heater circuit is necessary before taking any action needed.

Cause #4: Faulty Coolant Temperature Sensor

ECT is a vital engine component that measures the coolant temperature of the engine control unit. In return, the ECU adjusts the air-fuel ratio based on the temperature data it receives from the ECT. 

If the ECT gets faulty, it results in engine problems, thus setting up the P0135 to send an alert.

Symptoms of faulty engine coolant temperature sensors:

  • Check engine light on
  • Electrical cooling fans failure
  • Poor mileage
  • Engine overheating
  • Black and smelly smoke from the exhaust pipe

In order to solve this issue, you need to replace the engine coolant temperature sensor. The ECT sensor is pretty cheap; hence it can cost a few dollars to fix the problem yourself.

Cause #5: Faulty PCM (rare)

As mentioned above, oxygen sensors transmit optimal operating data to the PCM so as to regulate the air-fuel ratio. If the PCM malfunctions, it fails to receive signals from the heating component within the O2 sensor 1, thus triggering the P0135 code. Sometimes, this issue triggers P0135 plus P0300 codes.

However, a faulty PCM is a rare cause; hence it should be the last thing to verify after checking other possible causes of P0135. In case the PCM is bad, you need to engage a qualified mechanic to fix the problem. The issue is complicated, and it’s not easy to fix unless you are professional mechanical.


How Much Does It Cost To Fix The Code P0135?

The cost of fixing the P0135 code depends on whether you are using mechanic services or doing it yourself. Fixing the code on your own can cost a few bucks. For instance, replacing the oxygen sensor can cost $20 to $100.

Mechanic services tend to be more costly than DIY because of the labor cost involved. Usually, the labor costs are charged per working hour, and it can cost about $50- $150 depending on the car model and the mechanic rates. 

Refer to the table below to discover the most common DIY and mechanic cost of fixing P00135 based on the specific causes.

The Estimated Repair Cost Of P0135

SolutionsRepair cost
Replacing the oxygen sensorDIY: $20- $95
Mechanic: $100- $450
Fixing the oxygen sensor’s wiringDIY: $10- $25
Mechanic: $40- $75
Replacing the coolant temperature sensor

DIY: $10- $30
Mechanic: $85-$170

Replacing O2 sensor heater fuseDIY: $5- $20
Mechanic: $35- $70
Replacing the PCMDIY: Not recommended
Mechanic: $1,000- $3,000

Note: The data in this table was collected in July 2022. The actual price depends on many factors, such as your car’s make and year, mechanic’s rate, etc.


You Ask, I Answer

By reading this article up to this end, hopefully, you can now tell why you are receiving the P0135 code from the scanner tool. 

In case you have any burning questions, don’t hesitate to air them out via the Comment box below.

Also, I would like to hear your experience if you had the P00135 code before. What techniques did you use to fix the issue?

See yah!