What is the Air Fuel Ratio Sensor all about?
The air fuel ratio, or AFR, sensor is slowly replacing the traditional oxygen, or O2, sensor in late-model vehicles. It is more technologically advanced than your typical O2 sensor and, thus, delivers more precise air/fuel ratio management.
Similarities between AFR and O2 Sensors
Both determine if the engine is running too rich (too much gas in the air fuel mix) or too lean (not enough gas) by measuring the amount of oxygen in the exhaust. Each then reports that measurement back to the engine control unit, or ECU, which uses the data to make corrections to the air/fuel mixture so that it’s always perfect no matter what the environment or load on it.
Both are found in the exhaust manifold downpipes before the catalytic converter or between the exhaust manifolds and the catalytic converter.
The Difference between AFR and O2 Sensors
- The AFR sensor not only tells the ECU if the mix is rich or lean, but how rich or lean it is. Consequently, it's easier for the ECU to more accurately adjust the air/fuel mixture without overshooting and lots of guess work.
Keep in mind:
- Nearly one in ten Check Engine lights is caused by a malfunctioning AFR or oxygen sensor, and a faulty AFR or oxygen sensor can cause up to a 40 percent drop in fuel economy.
- When the fuel mix is rich there will be fuel left in the cylinders after combustion. This unburned fuel creates pollution.
- If there is excess oxygen, the mixture is referred to as lean. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, can cause poor performance and even engine damage.*
How it's done:
- The vehicle is supported on jack stands and the air fuel ratio sensor or sensors are identified and located
- The electrical connectors for the sensors are disconnected
- The air fuel sensor is removed and replaced with a new one
- The electrical connector is connected and secured
- The vehicle is lowered off of the jack stands and computer system is cleared of codes
The goal of the AFR sensor is to help the vehicle perform better and more efficiently, while emitting fewer noxious gases. When it fails your car ends up performing poorly, and it costs you more at the pumps. Plus, rich or lean doesn’t matter; both conditions can shorten the life of the expensive catalytic converter. So all vehicles manufactured in the last fifteen years should have their AFR sensors replaced every 60,000 to 90,000 miles. Replacing them at these intervals will lower your vehicle’s emissions and prevent more costly damage from occurring.
What common symptoms indicate you may need to replace the Air Fuel Ratio Sensor?
- Poor fuel economy
- Reduced engine performance
- Check Engine light is on
- Rough idle
- Engine misfires, hesitates, and/or pings when attempting to accelerate.
How important is this service?
The air fuel ratio sensor plays an important role in the optimal operation of your vehicle. A malfunctioning AFR sensor can cause a 40 percent drop in fuel economy as well as power loss, make your vehicle slow to accelerate, and eventually foul your spark plugs and eventually your catalytic converter, which is a much more costly repair than a sensor.