Air-Fuel Ratio (AFR) Sensors and Oxygen sensors (O2 sensors) are used for Air-Fuel Ratio (AFR) monitoring and control. Air-Fuel Ratio (AFR) Sensors are alternatives to oxygen sensors (O2 sensors) in modern motor vehicles. Air-Fuel Ratio Sensors are more technologically advanced with extra exceptional internal circuitry for precise air/fuel ratio of the engine.

Air-Fuel Ratio (AFR) Sensors Vs Oxygen Sensors

Modern vehicles and power-train engine control modules (PCM) using Air-fuel ratio sensors instead of oxygen sensors. Because lowering exhaust emissions and increasing fuel economy continues to be the aim of import manufacturers, a much wider range of air/fuel ratios must now be measured than is possible with the conventional oxygen sensor. Both, however, generate a similar signal for the power-train control module (PCM) to process.

The task of the air fuel ratio sensor is just that same as that of the oxygen sensor, which is controlling the oxygen levels in the exhaust. The difference is that, the output signal from the air fuel sensor is not changed right when the air/fuel mixture goes rich or lean. The advancement of the air fuel ratio sensors is very ideal for the low emission engines as well for tuning performance engines.

With either sensor, however, the engine’s PCM measures air/fuel ratios by monitoring a very small current that flows through the AFR sensor. A stoichiometric or chemically correct air/fuel ratio of 14.7:1 generates zero current flow through the AFR sensor. If the mixture is rich, a negative current flow is returned to the PCM. A lean mixture returns a positive current flow to the PCM.

Zirconia oxygen sensors and Titanium oxygen sensors are two types of oxygen sensors. Zirconium sensor and Titanium oxygen sensors are narrow-band oxygen sensors. The main problem with any narrow-band O2 sensors is that the Engine Control Module (ECM) only detects that the mixture is slightly richer or leaner than 14.7:1. AFR sensor is a wide-band oxygen sensor with high sensitivity to put the ECM in a better position to control the air/fuel mixture.

AFR sensors are located in the “pre-catalytic” converter or upstream position and a conventional narrow-range oxygen sensor is located in the “post-catalytic” or downstream position. The basic function of the upstream sensor is to maintain fuel control, while the basic function of the downstream sensor is to monitor the efficiency of the catalytic converter. The PCM monitors catalytic efficiency by comparing the data from the upstream sensor to that of the downstream sensor.

For some vehicle applications, the downstream sensor may also serve in a fuel control capacity. If the upstream sensor fails, the downstream sensor may act as a back-up fuel control sensor. In other operating conditions, the downstream sensor may actually act in concert with the upstream sensor to help control air/fuel ratios. This is a very application-specific feature and may only function in certain circumstances.