The first-generation Mazda3 (code BK), launched in 2003 to replace the aging 323, marked a major turning point for the brand. Based on Ford's excellent C1 platform (shared with the Ford Focus Mk2 and Volvo S40/V50), it immediately distinguished itself with its driving dynamics, precise steering, and sporty design. A facelift occurred in mid-2006, bringing slight aesthetic touches, improved sound insulation, the introduction of a 6-speed manual gearbox on the 2.0 diesel, and a very slight improvement in anti-corrosion protection (which remains the model's Achilles' heel). Although the gasoline engines are exemplarily reliable, the diesel versions (MZ-CD), very popular in Europe at the time, require extreme vigilance due to major design flaws, particularly on the 1.6 of PSA/Ford origin.
The Mazda3 BK is a car with two faces. As a gasoline model, it's a fantastic, reliable, fun-to-drive, and affordable compact. As a diesel, it's a minefield. The 1.6 MZ-CD (PSA-sourced) suffers from turbo lubrication defects related to injector seals, while the 2.0 MZR-CD (Mazda) is plagued by its DPF system which dilutes engine oil. If you're looking for a Mazda3 of this generation, avoid the diesels unless you have a service history as thick as a phone book proving that chronic defects have been addressed. Absolutely prioritize a gasoline model (1.6 or 2.0 MZR). In any case, the number one enemy remains corrosion: an inspection on a lift is mandatory before purchase.