Mercedes Benz Workshop Service and Repair Manuals

Oxygen Sensor: Description and Operation
O2 Sensors, Location/Task/Design/Function

O2 Sensors, Location

O2 Sensors, Position

Engine 111.951/55 Low emission EURO3 
G3/2 

O2 sensor upstream of TWC

Engine 111.951/55 Low emission EURO3 
G3/1 

O2 sensor downstream of catalytic converter

Engine 111.951 low emission D4 
157 Firewall catalytic converter 
G3/2 

O2 sensor upstream of catalytic converter 

G3/1 

O2 sensor downstream of catalytic converter