All vehicles come equipped with small engine components called engine oxygen sensors. Many different types of oxygen sensors perform an array of different functions, and a faulty oxygen sensor can wreak havoc on engine operation and performance.
Rough Engine Idle
Vehicle engines that have a bad oxygen sensor often run irregularly or roughly. Oxygen sensors can control or contribute to many different engine functions, including fuel/air mixture, engine timing and engine combustion intervals. A faulty oxygen sensor can disrupt any of these things and cause a rough engine idle.
A bad oxygen sensor can impede the air/fuel mixture of an engine or interfere with the engine combustion, both of which can cause an engine to miss, or run irregularly. An engine miss is normally most pronounced at idle or at lower engine speeds; a faulty oxygen sensor can inhibit the normal fuel delivery/combustion within an engine and cause a miss.
If a bad oxygen sensor is aligned with the ignition system on a car's engine, it can retard or advance engine ignition timing, which can cause an engine to ping. Pinging occurs when an engine's combustion gases are ignited at the wrong times.
Poor Gas Mileage
Depending on the type and/or location of a faulty oxygen sensor, the fuel-delivery and the fuel-combustion systems can be thrown off or made irregular by a faulty oxygen sensor. If too much fuel is injected into an engine's cylinders or a faulty oxygen sensor disturbs the delicate air/fuel mixture of an engine, gas mileage will suffer.
Increased Vehicle Emissions
Vehicle oxygen sensors play a critical part in keeping a vehicle's emissions within certain parameters. A vehicle can fail a state-mandated smog test because a bad, or faulty, oxygen sensor will not accurately measure various engine ratios or air/fuel mixture concentrations or adjust certain engine operations accurately enough to keep a vehicle's emissions in check.