Mercedes-Benz OM640

Mercedes-Benz's 2.0 CDI for the W169 A-Class and W245 B-Class — a transverse diesel in a sandwich-floor body, which is the fact that governs every job on it.

These cars carry the engine tilted, low, and above a double floor designed for crash protection, so access bears no resemblance to the longitudinal CDIs of the same period. A procedure written for a C-Class does not describe this installation, and quoted labour that looks disproportionate usually is not.

It carries the CDI family's injector-seal problem. The copper washer fails, combustion gases carry soot up around the injector, and it eventually seizes in the head — the sooty crust is the diagnosis rather than dirt, and treating seals as a service item rather than a repair is what avoids the expensive version.

The turbocharger's vane actuator sticks with soot, producing a limp home under load, and on short-journey cars the particulate filter cannot complete a regeneration — which dilutes the oil with fuel and eventually blocks the filter. These are city cars, so that duty cycle is the normal one rather than the exception.