How Does an Air Fuel Ratio Meter Work?

fuel filter

An air fuel ratio meter is a component in the engine that works to ensure that the mixture of fuel and oxygen in your engine is at the correct level, creating a situation where the combustion process works properly. To ensure that your vehicle continues to run smoothly, it is worthwhile understanding how the system works.


The chemical mixture of air and fuel in an engine needs to be correct so that they are consumed equally and keep the engine running effectively. No system is perfect, so this will not always be possible and a small level of oxygen often remains, which is what is measured by the air fuel ratio meter. The resulting reading is provided as an A/F ratio and works by way of the vehicle’s electrical system. Maintaining the correct A/F ratio ensures that the vehicle operates at an efficient level, which helps to reduce the level of emissions that are produced.


The air fuel ratio meter makes up part of the engine installation and is comprised of several LED lights that variously illuminate and dim to display the levels of air and fuel. The meter also makes use of sensors to read the levels of the air and fuel. The sensors are set at a level of sensitivity that enable accurate readings to be provided.


The sensors of the air fuel ratio meter are linked to the voltage of the vehicle’s computer system, which adjusts as and when it is necessary. The lower the level of oxygen, the higher the voltage gets, and the richer the A/F ratio becomes. When the voltage reaches a level of .450V, the meter works to reduce the amount of fuel to the engine by controlling the injectors. As the A/F ratio becomes leaner, the voltage gets higher, and the fuel injectors are released.


The ratio meter is constantly in operation to continually read the oxygen levels. The combustion process often does not work as it should and causes there to be air remaining because the fuel has been burnt off quicker. Due to the number of readings that the sensor takes and the speed in which they are obtained, there will be a number of results, and they will continually change due to the sensitivity of the sensors. When the throttle is wide open, the A/F ratio becomes rich due to the greater need for fuel and decreases the voltage. Reducing the speed of the vehicle will create a leaner A/F ratio, reducing the emissions produced by the vehicle.


To ensure the air fuel ratio meter works properly, there must be several conditions in place. As well as a reliable power source, the meter must be fitted so that it is properly grounded. The sensitivity of the sensors means that they can be affected by contaminants, such as carbon, lead particles and silicone. These can also cause the life span of the meter to be shortened. It should normally last approximately 50,000 miles.