Key Takeaways

  • A P1135 code means that there’s an issue with the air/fuel ratio sensor.
  • Air Fuel Ratio Sensor measures the air fuel ratio in an internal combustion engine.
  • Replacing an Air Fuel Ratio Sensor usually repairs the p1135 code.
  • Sometimes, wiring may need to be done in order to fix the issue.
  • Sometimes, the ECM of a vehicle may need to be replaced to fix a p1135.

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If your check engine light is on, it means your car is throwing a code. But what does a P1135  Toyota code mean, exactly?

A P1135 code means that there’s an issue with the air/fuel ratio sensor circuit in bank 1. This code is typically triggered when the engine control module detects the A/F sensor is not outputting voltage as expected.

I’m a mechanic with five years experience diagnosing and repairing vehicles. I received my associates degree in automotive repair. I am ASE certified and have received 20 credit hours of advanced diagnostics courses. I receive the most up-to-date training on the newest automotive technology, and use the latest tools to repair vehicles to this day.

Table of Contents


P1135 is a OBDII diagnostic trouble code that indicates a problem with the air/fuel ratio sensor circuit in bank 1, sensor 1.

The code is typically triggered when the engine control module detects that the air fuel ratio sensor is not providing the expected voltage output.

The air/fuel ratio sensor is responsible for measuring the oxygen content in the exhaust stream and sending this information to the ECM.

Once the ECM has this information, the ECM adjusts the vehicle’s air/fuel ratio to provide the vehicle with optimum fuel efficiency and emissions control. A P1135 code is specific to cars manufactured by Toyota.

When a P1135 code is detected, it can cause a variety of symptoms. Symptoms include reduced engine performance, and increased emissions.

Common causes of a P1135 code could be a faulty air/fuel ratio sensor, wiring or electrical issues in the air/fuel ratio circuit, or a problem with the ECM itself.

Air Fuel Ratio Sensor

The Air Fuel Ratio Sensor measures the air fuel ratio in an internal combustion engine. The sensor is typically located in the exhaust stream of an automobile.

The device works by measuring the oxygen in the exhaust. The AFR sensor takes this information and sends it to the vehicles Engine Control Module (ECM).

Based on the information that the AFR sensor reads, the ECM then adjusts the air fuel mixture of the vehicle to achieve optimal engine performance during idling and while under engine load.

The AFR, usually made of ceramic and other precious materials, is built to withstand high temperatures. The AFR sensor is in the exhaust stream, usually located close to the engine’s exhaust ports.

The sensor works by creating a voltage signal that it sends to the ECM. When the sensor is exposed to oxygen, it generates a voltage output that is interpreted as a lean air/fuel mixture.

When the sensor is exposed to a high concentration of fuel and a low concentration of oxygen, the sensor sends a signal to the ECM that is interpreted as a rich air/fuel condition.

The ECM constantly adjusts the vehicle’s air/fuel ratio based on information provided by the sensor.

These constant adjustments help ensure the vehicle is operating under the most optimal conditions, and ensure emissions are at a minimum.

An AFR sensor has a heater element circuit in the sensor. This heater element circuit heats up the sensor so it can start operating correctly as soon as the car starts. The sensor needs to be at a minimum operating temperature for it to operate correctly.

Otherwise, the sensor will give faulty readings.

Common Causes Of P1135

The most common causes of a P1135 code are a fault air fuel sensor, a shortened air fuel ratio sensor, or a problem with the ECM itself. Here are some common causes explained more in depth.

  1. Faulty Air/Fuel Ratio Sensor: Overtime, the air/fuel ratio sensor may become worn or damaged. This leads to inaccurate readings and causes a P1135 code to be triggered by the vehicle's ECM. The sensor should be providing an accurate voltage signal.
  2. Wiring or electrical issues: code p1135 can be caused by corroded or damaged wiring. Faulty electrical connections in the sensor heater circuit or AFR sensor circuit can cause the sensor to malfunction and can trigger a p1135 code.
  3. ECM Problems: In rare cases, the ECM may be receiving accurate signals, but might be outputting the wrong information. In this case, the p1135 code may be caused by an issue with the ECM itself. This can happen if the programming of the ECM has become corrupt.

These cover pretty much all of the causes of a P1135. If you have a P1135 and know your way around a car, you can start looking here. If any of this sounds foreign to you, make sure to take your vehicle to a mechanic to get rid of the P1135 code, as you risk doing more damage to your vehicle.

How To Fix A P1135 Code

If you are experiencing a P1135 code, it’s a good idea to take the vehicle to a qualified mechanic in order to fix it. Here are the steps a mechanic would take in order to repair a P1135 code.

  1. Diagnosis: The mechanic usually has specialized tools to help in the diagnosis of trouble codes. They will usually hook a OBDII reader up to the car to pull the code, and verify that the issue is in fact a P1135 code.
  2. Sensor Replacement: If the sensor is found to be faulty, the mechanic will remove the old sensor and replace it with a new one. This procedure takes about an hour maximum, depending on where the sensor is located and how rusted in the sensor is. If you do this yourself, be sure to check for exhaust leaks after.
  3. Wiring Issue: If the issue found is to be a wiring issue, the repair difficulty level just increased. The mechanic may have to repair the wiring through the use of soldering. A related wiring harness may have to be replaced as well.
  4. ECM replacement: If the voltage signal received by the ECM is correct, but the computer is still throwing a code, it’s time to replace the ECM. Replacing the ECM can be an easy job or a difficult job depending on where the ECM is located. The repair importance level of replacing an ECM is very high.

These are the main ways to fix a P1135 code. If you do not have tools, or know your way around a vehicle, it’s best to bring your car to a qualified mechanic.

But all of these jobs are not that difficult.

They pretty much involve just removing and replacing parts.

Except wiring. Wiring can be a hassle, especially if you want your car performing at factory specifications.

P1135 Toyota Code Information, Causes & Fix

About The Author

Christopher Sparks

Christopher Sparks

Christopher Sparks has been servicing vehicles since 2012. After completing the automotive studies program at Camden County College, he was awarded an Associates's Degree in Applied Science. His first job was a lube-tech at Jiffy Lube, and is currently an independent B-Technician servicing vehicles for the United States Postal Service. Christopher is ASE certified and loves rebuilding engines.

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