Oxygen Sensor
WARNING: This page is about a different car, the 1993 Mercedes-Benz 300E. However, it is still accessible from the selected car via links, so may be relevant.
These vehicles use 2 oxygen sensors. The oxygen sensors measure residual oxygen in exhaust gas. The oxygen sensors send (C)a voltage signal to engine control module. The engine control module uses oxygen sensor voltage to control fuel injection.
O2S 1 is located before the catalytic converter in the exhaust system. O2S 2 is installed in the exhaust system after the catalytic converter. The function is identical to O2S 1. However, O2S 2 signal is used to monitor the efficiency of the catalytic converter and function of O2S 1.