The second-generation Smart Fortwo (code name W451) succeeds the W450, growing by 19 cm to improve safety (crash tests) and comfort. It abandons Mercedes-Benz petrol engines for 1.0L 3-cylinder blocks of Mitsubishi origin (3B2 family), but retains a Mercedes-Benz diesel engine (OM660), which is the focus of this report. This 0.8 cdi block holds the title of the smallest mass-produced diesel engine in the world. While the Tridion safety cell remains a benchmark, the overall reliability of the 451 is marred by poor statistics: ADAC notes a breakdown rate of 4.1/1000 vehicles/year (below average), the TÜV Report points to a 3-year defect rate of 21.5% (among the worst in the segment), and What Car? gives it a reliability rating of 2/5 (35% breakdown rate over 12 months). The automated gearbox