Genuine Bosch oxygen (lambda) sensor for the Mercedes-Benz M271/M274 turbo four-cylinder family. Mounted pre-catalytic-converter, it continuously measures exhaust oxygen content so the ECU can trim the air-fuel mixture for efficiency and emissions compliance; a 5-wire design with a vehicle-specific connector and a recommended replacement interval around 250,000 km.

Fitment: Mercedes-Benz E-Class (W212/S212) and C-Class (W204) with the M271 CGI / M274 1.8L-2.0L turbo engine (confirm exact model year and sensor position - pre vs. post-cat - at checkout).