Mercedes-Benz B-Class Lambda Sensor Replacement Parts

Yes, but only on petrol-engined B-Class models — the lambda (oxygen) sensor is part of the exhaust emissions system that monitors combustion on petrol engines. Diesel B-Class variants (such as those running the OM640 or OM651 engine families) do not use a lambda sensor in the traditional sense, as diesel engine management works differently. If you have a diesel B-Class and are chasing an emissions or running fault, you are more likely looking for a NOx sensor, exhaust temperature sensor, or something related to the DPF or EGR system — confirm with your breaker what your engine code is before ordering anything.

These are different generations — the W245 ran from 2005 to 2011 and the W246 from 2012 to 2018 — and while both generations offered petrol engines, the engine families changed between them, meaning the sensor specification, connector type, and thread pitch may well differ. The generation boundary here is a firm fitment boundary, and crossing it with a used lambda sensor is not straightforward. Always quote your engine code (for example M270 on the W246 petrol) to the breaker alongside your registration so they can match the correct sensor position and specification.

The W246 received a facelift in 2015, but for the lambda sensor what really matters is your engine code and fuel type rather than whether your car is pre- or post-facelift — the sensor follows the engine, not the styling update. If the engine code remained the same across the facelift on your specific variant, the sensor is likely the same part, but you should still give the breaker your exact engine code and registration to confirm, as emissions calibration can sometimes change even within a generation.

No — trim level does not affect lambda sensor fitment on the B-Class; Sport, SE, AMG Line, and Urban are cosmetic and equipment packages that do not change the exhaust or engine management setup. What determines the correct sensor is your engine code and fuel type, so a lambda sensor from an SE-spec car with the same engine code as your AMG Line is the same part. The only thing to watch for cosmetically is that AMG Line or sportier trim cars sometimes look different under the bonnet or at the exhaust, but the sensor specification itself is engine-driven, not trim-driven.

Most petrol B-Class engines run both an upstream (pre-cat) and downstream (post-cat) lambda sensor, and they are different parts — the upstream sensor usually has a shorter lead and different calibration to the downstream one, so you need to identify which position has failed before ordering. A breaker will need your engine code, your registration, and ideally confirmation of which sensor position (upstream or downstream, sometimes called sensor 1 or sensor 2) is flagged in your diagnostic report. Getting this wrong means buying the right-looking part for the wrong location, so be specific with the breaker.

Euro 5 and Euro 6 represent a genuine emissions era boundary, and while the physical sensor may appear similar, the calibration and engine management requirements for Euro 6 compliance are tighter — fitting a Euro 5 sensor to a Euro 6 car risks incorrect fuelling, failed emissions readings, and potentially an MOT failure. The W246 spans this boundary, with Euro 6 variants appearing from around 2014–2015 depending on engine, so it is entirely possible to find two W246 petrol B-Classes that look identical but sit on different sides of that line. Give the breaker your engine code and confirm the emissions standard of the donor vehicle before purchasing a used sensor.