When to replace Oxygen Sensors

Your vehicle’s oxygen sensors play an important role in the optimal operation of your vehicle, but these parts are often overlooked when performing regular vehicle maintenance. The main reason for this is because many automobile owners do not know the symptoms of bad oxygen sensors, and only learn of the issue when the check engine light sparks up on their dashboard or their vehicle fails an emissions test. The role of your oxygen sensor is simple; it performs tests on your car’s exhaust to determine how much oxygen is in it. It then transports the data to your vehicle’s computer, which uses the findings to create the perfect air to fuel mixture for optimal engine performance. On top of poor engine performance, a bad oxygen sensor will have an increased negative impact on the environment as it releases higher levels of pollution into the air

That is all fine and dandy, but you probably want to know when to an replace oxygen sensor on your car or truck.

O2 sensors are a relatively inexpensive part to replace on your vehicle. If you have a suspicion about your part being faulty, it is best to change it earlier than later. It is not very common for an O2 sensor to completely fail, as it more often fails over time. If you do not know failing oxygen sensor symptoms, you will not be able to diagnose the problem until it completely fails. In the meantime your vehicle will suffer from poor engine performance which can have long term effects on your engine life. Typically, mechanics have recommendations on the replacement intervals for these parts. Cars and Trucks from the 1970’s to 1990’s that were equipped with unheated one or two wire oxygen sensors should have the part replaced around the 45,000 mile mark. For automobiles that were manufactured in the 1980’s to 1990’s, and were equipped with heated three and four wire oxygen sensors, it is recommended you replace the part every 65,000 miles. All cars and trucks that were manufactured in the last fifteen years should have their O2 sensors replaced every 60,000 to 90,000 miles. Replacing your sensor at these intervals will lower the level of pollution that your vehicle emits while playing a preventive role in the cause of damage to the vehicle.

Every new car, and most cars produced after 1980, have an oxygen sensor. The sensor is part of the emissions control system and feeds data to the­ engine management computer. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.

A gasoline engine burns gasoline in the presence of oxygen (see How Car Engines Work for complete details). It turns out that there is a particular ratio of air and gasoline that is “perfect,” and that ratio is 14.7:1 (different fuels have different perfect ratios — the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If there is less air than this perfect ratio, then there will be fuel left over after combustion. This is called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If there is more air than this perfect ratio, then there is excess oxygen. This is called a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, it can cause poor performance and even engine damage.

Th­e oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage (see the patents below for details). The engine’s computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.

The reason why the engine needs the oxygen sensor is because the amount of oxygen that the engine can pull in depends on all sorts of things, such as the altitude, the temperature of the air, the temperature of the engine, the barometric pressure, the load on the engine, etc.

When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to.