How to Check and Replace an Oxygen Sensor

Oxygen sensors (Air fuel ratio sensors) are a common problem on many vehicles. A P1155 or P1135 code indicates you have a bad sensor. This is common in Toyota and Lexus cars and trucks. Learn how to test the air fuel ratio sensor to see if it is bad, and then learn how to replace the bad sensor.

Some background info on difference of Oxygen Sensors and Air/Fuel Ratio Sensors. What distinguishes Air Fuel Ratio Sensors from regular O2 sensors is that the AFR Sensor is what is known as a wide range O2 sensor whereas the basic O2 sensor is a narrow range sensor. It can detect a wider range of air/fuel ratios than the basic O2 sensor. Also, the AFR Sensor has a little bit more circuity to enable it to detect more minute variations in the exhaust system air content (more sensitive than the O2 sensor). Therefore, it is able to make better adjustments through the ECM to add or subtract fuel to produce a better mix of air/fuel to maximize efficiency and minimize emissions.