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It measures how much oxides of nitrogen your vehicle is releasing and feeds that data to the SCR system, which then adjusts the emissions output so it stays within legal limits.

It's most commonly fitted after the SCR catalyst, so the system can
confirm NOx levels have dropped to a compliant amount. Some vehicles
also have a second sensor positioned before the catalyst.

No. While they're most common on diesels, most modern petrol vehicles
have at least one NOx sensor too, since emissions rules apply to both
fuel types.

The most common cause is a build-up of soot from the combustion process. Soot can coat the sensor and stop it from reading gas levels accurately, and over time it can cause physical damage too.

Common signs include the engine warning light coming on, higher fuel consumption, reduced power, the car going into limp mode, sluggish acceleration, and an overall drop in performance.

Not recommended. NOx sensors are designed to be self-cleaning, so if one is showing signs of failure, replacing it is the correct fix rather than trying to clean it manually.

Repairing can seem like the cheaper option, but for such a precise component it's usually only a short-term fix. Replacing it properly the first time saves you doing the job twice.

We'd always recommend a brand new sensor over a refurbished one. New components give you the most accurate readings and the longest lifespan.

Yes. Since NOx sensors are tied directly to emissions compliance, a fault can push your vehicle's emissions output outside legal limits, which can result in an MOT failure.

Always check your vehicle's make, model, engine code and year before ordering. If you're unsure, our team is happy to confirm compatibility before you buy.