The Ultimate Toyota Oxygen Sensor Buyer's Guide

If you've got questions about oxygen sensors, you've come to the right place! This buyer's guide explains everything you need to know about oxygen sensors, including how to diagnose problems and what to do if one of your oxygen sensors fails. It also explains why OEM oxygen sensors are better than aftermarket products and how they can save you money. 

What's An Oxygen Sensor, How Does It Work, and Why Is It Important?

An oxygen sensor is a small, tube-shaped sensor mounted in the exhaust system. It registers the amount of oxygen in the exhaust gasses and relays that information to the ECU. The ECU uses that information to adjust the air/fuel mixture for optimal engine performance. Your exhaust system has up to four oxygen sensors depending on the engine size and exhaust layout. If one fails, your ECU will not receive accurate information on your engine's emissions and may end up reducing your engine's performance. Read more about oxygen sensors and how they work here.

How to Diagnose a Failing Oxygen Sensor

It's not uncommon for an oxygen sensor to fail. Typical symptoms include a rough idle, sluggish acceleration, and the engine running hotter than normal. In addition to these symptoms, your check engine light should come on, and the ECU will record one or more of the following OBD-II codes:

  • A P2270 code represents a fault in the air/fuel sensor circuit that is causing it to run lean in bank 1, sensor 2. One of the more common reasons for this code is an oxygen sensor malfunction, but it could also be related to other problems like a fuel injector problem, a vacuum leak, or other sensor malfunctions. 
  • A P1135 code is triggered when the ECM detects a malfunction in the oxygen sensor heater circuit. The problem could be due to an air/fuel ratio sensor bank or a bad electrical connection, but an oxygen sensor failure can also cause it.  
  • Error code P0420 is one of several trouble codes that fall into the general exhaust system code block. It refers to the catalytic converter or the oxygen (O2) sensors before and after it on the bank one side of the exhaust system.
  • P0171 System Too Lean - This code is one of the most common trouble codes in V-6 and larger engines. It is triggered by the first exhaust oxygen sensor on the "Bank 1" side of the engine.   

Even if you're experiencing all of the symptoms, it's still a good idea to officially confirm that your oxygen sensor is broken before replacing it. The way to do this is to test all of your oxygen sensors with a digital voltmeter. This comprehensive tutorial covers all the steps of the diagnostic process.

Are OEM Oxygen Sensors Better Than Aftermarket?

Are you on the fence between buying an OEM oxygen sensor or an aftermarket oxygen sensor? This comparison guide should help you reach a decision. In a nutshell, OEM is the safer bet and can save you money down the road.

How to Replace Your Toyota's Oxygen Sensor

Replacing the oxygen sensor in your Toyota is a simple process requiring a 22-millimeter wrench and anti-seize lubricant. This tutorial covers all the steps to replace your oxygen sensor safely and efficiently. Or you can use this guide which provides more information on signs of a bad O2 sensor and how to replace one. 

How Are Oxygen Sensors Different From Air/Fuel Ratio Sensors? 

An air/fuel ratio sensor is much like an oxygen sensor, or O2 sensor, and is slowly replacing them on many vehicles. They are located in the same positions as oxygen sensors but are more accurate to meet the needs of today's engines. This helpful guide explains how air/fuel ratio sensors work and how they are different from oxygen sensors.