The N43 (four cylinder) and the N53 (six cylinder) are direct injection petrol engines built for lean burn operation. Lean burn demands far more of the injection system than a conventional port injected design, and these are exactly the three parts that gave trouble in service: the injectors, the ignition coils and the NOx sensor.

You notice this as a rough, uneven idle, hesitation on a cold start, loss of power and higher fuel consumption. A faulty NOx sensor on its own also raises consumption, because the control unit then fuels for the worst case.

The piezo injectors are expensive each, and when one fails the replacement rarely stops at one. The N53 also uses the same high pressure pump as the N54, where pump failures led to litigation in the USA. Pump failures were reported on the N53, but it is not known whether they are as frequent as on the N54 (the N53 was not sold in the USA, so there is no official complaint data on it).