Oxygen (O2) Sensor

O2 sensor (located in top of exhaust manifold) monitors oxygen content of the exhaust and supplies logic module with a voltage signal which is directly proportional to this content. If oxygen content of the exhaust is high (lean air/fuel mixture), voltage signal from sensor to logic module is low. As oxygen content decreases (mixture becomes richer), signal voltage increases. Logic module can then alter fuel injector "on" time, in response to these signals, to obtain best air/fuel ratio.