An internal combustion engine is actually a fairly simple concept; combustion, otherwise known as burning, is the chemical process inside an engine where the ignition of a fuel and oxygen mixture creates energy for the engine to run. This combustion, however, requires a precise ratio of fuel to oxygen in order for the engine to function at peak performance with as few emissions as possible. This is where the oxygen sensor comes into play. Its main function is to monitor this fuel to oxygen ratio and report back to the engine management computer (EMC) so it can make any necessary adjustments to keep the engine running efficiently.

As it turns out, the perfect ratio of oxygen and gasoline is 14.7:1. If the oxygen sensor detects that there is too much oxygen left over after combustion, then the mixture is said to be “lean” and the EMC will adjust the amount of fuel entering into the engine accordingly. Lean mixtures can cause poor engine performance, engine damage and releases more nitrogen-oxide pollutants into the environment. On the other hand, if there is fuel left over after combustion, then the mixture is described as “rich” which will create excessive pollution due to the unburned fuel.

Since engineers already know the exact ratio of oxygen to gasoline needed for peak performance it might seem unnecessary to monitor it all the time. The problem is that the amount of oxygen an engine pulls depends 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. If the oxygen sensor is faulty, then the EMC has to guess how much oxygen and fuel to send to the engine which can cause the engine to perform poorly and decrease fuel efficiency.

Oxygen sensors perform an integral role in an engine’s operation and if they go bad or become faulty it is necessary to change them as soon as possible to prevent engine damage. If a vehicle’s oxygen sensor is bad, then the check engine light will usually go on, but there are other symptoms you can look for as well to determine if your oxygen sensor might be an issue. A misfiring engine, rough engine idle or an engine that hesitates during acceleration may indicate a faulty oxygen sensor. If you suspect your oxygen sensor might be going bad, take your vehicle into an auto repair shop and they can check it to see if that is an issue.