Oxygen Sensor Heater
WARNING: This page is about a different car, the 1992 Mercedes-Benz 400E. However, it is still accessible from the selected car via links, so may be relevant.
The temperature of oxygen sensor ceramic body is important because it affects conductivity of oxygen ions. The ceramic material becomes conductive for oxygen ions at approximately 572°F (300°C). Normal operating temperature for oxygen sensor is approximately 1112°F (600°C).
When coolant temperature is more than 95°F (35°C), LH control unit sends heating current to oxygen sensor. The heating current ensures oxygen sensor reaches operating temperature very quickly. The output of oxygen sensor heater is 18 watts.
Oxygen sensor heating is switched off when engine speed is more than 5500 RPM because hot exhaust gases are present. When engine speed is less than 5500 RPM, oxygen sensor heating is switched on again.