Smart ForTwo ED Brabus

The shift actuator (part no. A4518290201) controls the electronic gear selection. When it fails, individual gears are lost or the gearbox no longer shifts at all. Typical problem on older examples from 100,000 km.

The SAM control unit in the driver's footwell is susceptible to moisture ingress via leaking windows or door seals. Corroded solder joints (lead-free solder in early production years) cause failures. Vehicle does not start, warning lights flicker.

The 451 electric power steering is prone to failure due to worn carbon brushes or a stuck relay contact. In the worst case, the complete steering rack must be replaced. Sudden failure while driving is possible.

Recall of 90,889 vehicles (model years 2010–2014) due to possible short circuit in the heater shut-off valve. Vehicles where the recall was not carried out may pose a fire risk. Recall should have been performed free of charge at a workshop.

On the early 451 (before the 2010 facelift), the catalytic converter and rear silencer are a single unit. Typical short-trip use means condensation water never dries out, and the steel rusts from the inside. Replacement including fitting costs €600–1,200.

The 451 instrument cluster can show pixel failures or fail completely. Specialist repair services offer solder joint repairs. The instrument cluster is not just a display but also a control unit.

On early production years (up to 2009), faulty rain sensors caused parasitic drain that discharged the battery overnight. Mercedes resolved the problem by switching suppliers. Older examples may still be affected.

As a typical city car, the 451 is rarely driven far enough to warm through. Moisture remains under the plastic Tridion frame and promotes corrosion on suspension components, brake lines and the exhaust system. MOT inspectors flag this frequently.