To understand the importance of the oxygen sensor and why it is needed, we first need to understand how the engine itself operates. The basic concept of combustion engines is to add a tiny amount of fuel to a small enclosed space and ignite it; there is an incredible amount of energy released in the form of expanding gasses from this combustion which is utilized to power the vehicle. There have obviously been many changes since the first vehicle was created back in the 1800’s but one thing has remained constant, the four-stroke design of all combustion engines.

The four-strokes in each engine cylinder are broken down into the intake stoke, compression stroke, combustion stroke and finally the exhaust stroke. In the intake stroke, oxygen and gas enter the cylinder, the compression stroke adds pressure to this mixture, the combustion stroke ignites the mixture and during the exhaust stroke the exhaust is released out of the cylinder to eventually exit the tailpipe. Each cylinder in the engine goes through these four strokes hundreds of times in a minute, and there must be a precise mixture of gasoline and oxygen each time for maximum efficiency. This is where the oxygen sensor comes into play.

The oxygen sensor measures the exhaust from the cylinders and depending on the amount of oxygen remaining after combustion, sends a message to the engine’s computer to make adjustments. The perfect ratio of oxygen to gasoline is 14.7 to 1. When there is too much oxygen entering the cylinder during the intake stroke, it can cause poor engine performance, engine damage and will release more nitrogen-oxide pollutants into the environment. On the other hand, if there is too much fuel during the intake stroke, there will be unburned gasoline left over which will create excessive pollution and can ignite in the catalytic converter, causing it to fail which leads to a significant repair bill.

Every engine has a baseline set of parameters it utilizes to determine the amount of gas and oxygen to send to the cylinders but that amount fluctuates depending on a variety of factors. The air temperature, engine temperature, altitude, barometric pressure and even the load on the engine can all change how much oxygen is pulled into the engine. In order to maintain the perfect ratio of 14.7:1, the engine needs to make periodic adjustments, which it can only do if the oxygen sensors continue to send information. If the oxygen sensor is faulty, then the engine’s computer has to guess how much oxygen and fuel to send to the cylinders which can cause the engine to perform poorly and dramatically decrease fuel efficiency.

Most vehicles today have a minimum of two oxygen sensors; however some modern vehicles can have up to six or more. When one of these sensors fails, the Check Engine light will generally go on, but you might notice some other symptoms as well. A faulty oxygen sensor can lead to rough idling, hesitation during acceleration, engine misfires, engine surges or bucks, poor fuel economy, unexpected catalytic converter failure or a rotten egg odor emitted from the exhaust.

Replacing a faulty oxygen sensor is a fairly inexpensive repair, however if you put it off it could end up costing you quite a bit more in the long run. If it causes damage to the catalytic converter you will be looking at repair costs in the thousands instead of just a couple hundred. A bad oxygen sensor could also cause you your gas mileage to drop up to 40% as well, which at today’s gas prices is a huge chunk of change. If you suspect that your vehicle might have a faulty oxygen sensor, it is in your best interest to take it into an auto repair shop and have it checked out sooner rather than later; from the impact to your pocket book to the negative impact on the environment from excess pollution, it is well worth the price of replacement.