Mazda

The high-compression engine of Mazda3, Mazda6 and CX-5 (13:1 ratio). Direct injection favors valve deposits, and vacuum leaks trigger lean codes.

CX-5 and Mazda6 diesel with a two-stage turbocharger. A solid engine, but city driving means the DPF and EGR need regular regeneration.

The larger petrol unit of CX-5 and Mazda6 with cylinder deactivation. Failures are rare, mostly minor EVAP system leaks.