Wideband Oxygen Sensor
A precision oxygen sensor that provides a continuous range of air-fuel ratio measurements rather than a simple rich/lean switch.
A wideband oxygen sensor (also known as an Air-Fuel Ratio or AFR sensor) is a precision diagnostic sensor located in the exhaust pipe upstream of the catalytic converter. Unlike standard 'narrowband' oxygen sensors—which can only detect if the fuel mixture is rich or lean (switching back and forth like an on/off switch)—a wideband sensor measures the exact air-fuel ratio across a continuous spectrum.
Inside the wideband sensor is a specialized electrochemical 'pumping' cell that measures the amount of oxygen in the exhaust. It outputs a variable current signal to the ECU, which represents the exact AFR (such as 12.5:1 for maximum power or 14.7:1 for cruising). This allows the engine computer to make highly precise, real-time adjustments to the fuel injection system.
Failing wideband sensors can cause poor fuel economy, engine hesitation, black exhaust smoke, and check engine codes like P0130 or P2195. Because they operate at high temperatures, they have internal heaters that can burn out over time. Diagnosis involves using a scan tool to monitor sensor current readings and graphing its response to throttle changes.