N20B20 engine faults.

The chain guide of the early N20 engines is brittle: if it breaks, the chain goes slack, and from then on the timing is imprecise. The symptom is initially a high pitched whistle or drone from the front of the engine that rises with the revs: many people take it for the supercharger or a pulley noise. Later a metallic rattle on a cold start joins it.

The oil pump is driven by a separate, smaller chain from the crankshaft, behind the timing chain at the front of the engine. This chain runs on plastic guides, and under heat cycles the plastic cracks, flakes off and finally disintegrates. From then on the chain works against the aluminium, the tension is lost, and the stretch progresses fast.

A rubber gasket seals the oil filter housing to the block. The gasket hardens over the years, and oil leaks from under the housing. The oil drips onto the drive belt and the alternator.

The maker builds the charge pipe out of plastic, and the coupler at the throttle body is the critical point. The material goes brittle from heat cycles, from boost pressure and from the heat of the engine bay, and then it cracks. Three things coincide here: the moulded coupler carries both pressure and movement, the vibration of the engine arrives here through the throttle body, and the spot gets continuous heat load. The crack starts on the inner radius of the coupler. The symptom is a loss of pressure under load: the engine pulls cleanly at part throttle but flattens out at full throttle, and a hissing noise is audible from the engine bay at the same time. A yellow drivetrain warning comes with it, which often disappears after a restart, and sometimes a brief limp mode. One thing is worth knowing: a clean fault memory does not rule the crack out. The pipe has no sensor of its own, so the control unit can only log a boost pressure fault, and the leak is intermittent, appearing only under load. At a viewing two things are visible without tools. On the inner radius of the coupler the hairline crack sometimes comes with dark staining, because the oil mist in the boost air escapes through it. For the same reason a greasy, dark ring can appear at the joint of the coupler. The crack is reported above 80 000 kilometres, and replacing the pipe costs between 100 and 400 euros, because the part itself is not expensive. The most common misdiagnosis against that is replacing the turbocharger, which costs an order of magnitude more, and a pressure test protects against it. The factory repair is the same plastic part, which can crack again at a similar mileage; replaced with an aluminium pipe this failure mode disappears, and the driveability does not change.