P1135 Vs P1155 Toyota Avalon Code: Causes & How To Fix

During vehicle maintenance or oxygen sensor checks, you discover codes P1135, P1155 that you have never seen before. What are P1135 vs P1155 Toyota Avalon codes? Why do they appear? Are they serious problems with your vehicle? How to fix them? Let’s dig in and discover.

What Are P1135 Vs P1155 Toyota Avalon?

What Are P1135 Vs P1155 Toyota Avalon

During the design of Toyota vehicles, manufacturers provided each car with certain trouble codes. Each code represents a problem in a different part of the auto. It helps the mechanics know the cause of the issues and easily fix them.

The trouble codes are not the same for every vehicle. Depending on the model of the car, they have codes with different meanings. P1135 and P1155 are such DTC codes common in Toyota models, typically Toyota Avalon.

Toyota P1135 and P1155 codes

Toyota P1135 and P1155 codes – Image source: Carparts

What Does They Mean?

P1135 and P1155 codes pop up to signal that your car’s ground circuit (A/F sensor heater circuit) is open or failed.

Any car’s A/F (Air/Fuel ratio sensor) must achieve a specific operating temperature to provide precise power indications. Before that, it must reach a temp of at least 1200°F. The terms “oxygen sensors” and “O2 sensors” are other names for this A/F one.

The sooner it gets to the operational range, the quicker the sensor can transmit precise measurements to the ECM (Engine Control Module).

The A/F ratio sensor has a constructed heating element to help it attain the appropriate working temperature. It is used to monitor the exhaust’s oxygen content over a wide range.

The engine load and coolant temperature signals that the ECM receives are used to operate the A/F ratio sensor heater. Your car’s ECM detects and reads output voltages collected through the electric heating circuit to assess the circuit’s condition by measuring the voltage to manufacturing requirements.

The codes P1135 and P1155 will be activated if there is any problem receiving the signal related to the oxygen content through the exhaust manifolds.

What Is The Main Difference Between These Codes?

The auto system displays the P1135 error code when it notices a problem coming from the voltage signal. The heating element in the A/F ratio bank 1, sensor 1 (rear engine exhaust manifold), is the source of this indication.

Meanwhile, a widespread issue with the A/F sensor heating circuit in bank 2, sensor 1 (front engine exhaust manifold) is indicated by the P1155 code.

What Are The Causes Of These Codes Appearance?

The DTC P1135 Toyota code problems usually come from the faulty A/F ratio sensor in bank 1, sensor 1. A short, broken, or loose sensor wiring will cause the sensor to malfunction.

Also, if this air/fuel sensor has a poor electrical connection or the engine control module is faulty, the P1135 code will appear (because the ECM controls engine tuning, acceleration, as well as fuel efficiency of the vehicle).

ECM failure is the main culprit behind the code P1155. This code also appears when the circuit cables of the A/F in bank 2, sensor 1 malfunction. The circuit connections and worn or exposed wiring can trigger the P1155 code to appear.

A/F sensor connector

A/F sensor connector  

What Are The Symptoms Of These Codes?

Since these 2 codes both stem from problems related to the air/fuel ratio sensor in sensor 1, they will have some of the same symptoms when they appear. The easiest sign to detect is that the Check Engine Light stays on for a long time and does not turn off.

In addition, the inefficient engine is also a warning you can consider.

The P1135 code may appear when the engine is not operating properly. It will not work at full capacity or become unusually hot. However, the code P1135 may not be always associated with these symptoms. So, it’s best to take your car to a reliable repair shop for a thorough checkup.

The P1155 code is often followed by more indicators. The most obvious signs are difficulty starting the engine and loss of engine performance. In addition, uneven idling, poor acceleration, and markedly reduced engine power are also symptoms of the P1155 code.

How To Fix These Codes?

Preparation Steps

The first step is diagnosing the system. You can inspect the wiring and its connector to verify that no cables are broken. Next, ensure that nothing has come loose by checking the links.

The A/F ratio sensors are prone to heat damage and might also sustain damage by coming into touch with antifreeze or other fluids. Most are indeed designed to endure 50,000 miles before experiencing external damage.

After that, check if there are any air leaks, particularly close to where the A/F ratio sensor is installed. Also, examine this sensor’s electrical circuit elements for flaws caused by burns, rusting, or other issues.

Run voltage checks on the sensor circuit to ensure the power rating matches the manufacturer’s guidelines.

Fixing Steps

As of right then, the P1135 and P1155 error codes result from a problem with either the air/fuel ratio bank 1, sensor 1, or the A/F ratio bank 2, sensor 1.

You will have two choices: one option is to fix the ratio bank 1/bank 2 or change the entire sensor 1. If you cannot decide for yourself, you should ask an experienced technician or repairer. They will offer the most suitable option for your vehicle’s condition.

When you want to solve the problem yourself, you can refer to the following steps:

Step 1: Instead of replacing the whole sensor 1, you can check and replace the wiring yourself if you find them worn or broken.

Step 2: If a leak is found, replace it to prevent the vacuum exhaust from leaking.


Are These Codes A Serious Problem?

No. P1135 and P1155 codes are not a serious problem. They are just warning messages about your vehicle’s O2 concentration and A/F ratio sensor status. However, it will be best to fix it when possible, as it can signify wiring damage and other complications.

Therefore, DIY or go to the local garage or auto service center to have the technician or mechanic check it for you. If there is more serious damage, replace the damaged parts.

What Are Common Mistakes In Fixing The Codes?

When troubleshooting code P1135 or P1155, you may make some of the following errors:

  • Did not test the circuit or connector or did not test it thoroughly.
  • After replacing the sensor radiator, forget to check it again to avoid the error recurring or further damage.
  • Ignore the possibility of an exhaust leak near the A/F sensor. Some leaks are difficult to detect. But after dealing with other issues, the code still appears, then you should have a mechanic inspect and fix it.
  • Skip the scan and test drive.

Engine exhaust manifold

Engine exhaust manifold 

What Are Other Related Codes?

In addition to P1135 and P1155 codes, some other popular codes represent for other common problems:

P0102: Mass or Volume Air Flow Circuit Malfunction

P0107: Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input

P1131, P1135: Range Sensor Issues

P2242: Oxygen Sensor Pumping Current Circuit / High (for A/F sensor)

P3231: A/F sensor plus minus circuit correlation (Bank 1, Sensor 1)


What are P1135 vs P1155 Toyota Avalon Codes? They are error codes that appear when problems or failures appear in the A/F ratio sensor 1. While not a serious problem, you should find the cause and fix them. We hope you find this article useful. See you in the next posts!

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