AdBlue — / SCR (Selective Catalytic Reduction)

AdBlue is the brand name for a 32.5% urea solution that is dosed into the exhaust stream of modern diesels to reduce NOx emissions via the SCR catalyst reaction. The ECU monitors urea tank level, NOx sensor input pre and post-cat, and SCR efficiency.

AdBlue systems fail expensively: NOx sensors cost €400-800, urea pumps clog with crystallised urea, and the system has a built-in "limp home" countdown that locks the engine to 30 km/h (or no-start) once the tank is empty. Export and off-road operators delete AdBlue at the ECU level.