The common rail high-pressure pump is lubricated and cooled by the diesel itself, because the pump produces over 2,000 bar and has no separate lubrication circuit. If that lubricating film breaks down, the internal running surface of the pump eats itself and metal debris is produced. The debris travels through the whole system with the diesel, the rail, the injectors and the tank as well, because the return line carries it back and the lift pump draws it in again at every start. From there flushing the injectors does not help, all of them have to be replaced and the tank cleaned too. The failure is reported between 120,000 and 160,000 km, and the repair runs from 1,500 to 15,000 euro depending on how far the debris got. The lubricating film is broken by misfuelling and by long runs with an almost empty tank, because below 5 litres the lift pump also draws air. Plain wear of the pump is a different case: there is no debris and only the pump has to be replaced.

The timing chain of the longitudinal V6 diesel runs at the back of the engine, on the gearbox side, so replacing it means taking out the engine or the gearbox. That alone makes it expensive, but the mechanism is the point: the chains stretch and the hydraulic tensioners lose their pressure. The first and only early sign is a 2 to 3 second metallic rattle audible on a cold start. If that is ignored, the chain jumps or breaks, and the engine is badly damaged inside. The same chain kit also drives the oil pump: if that seizes, the engine is left without lubrication.

A small electric motor built into the rear brake calipers applies the parking brake. This is a known weak point of the B8 platform (A4 B8, A5 8T, Q5 8R, allroad B8): moisture and road salt get into the motor housing, the electronics corrode, and the gears seize. The symptom is a parking brake that will not apply or will not release, with a fault message.

The front suspension of the longitudinal engine Audis (and the Seat Exeo derived from them) works with four control arms per side: two above, two below. That gives excellent steering when new, but it also means four ball joints and eight bushes per side: sixteen wear points at the front in total.

The 7 speed wet clutch S tronic used in the longitudinal engine Audis (0B5 / DL501) is more durable than the early DSG units, but the mechatronics unit is the most common source of faults here too. As the solenoids wear, the regulation of the hydraulic pressure deteriorates: harsh or missed shifts, delayed D/R engagement, and finally limp mode.

The internal springs of the flywheel tire, and the two discs knock against each other. The signs are a rattling or knocking from the bellhousing at idle and when releasing the clutch pedal, and vibration through the floor. If the clutch slips without a burnt smell, that also points to the flywheel. It is worth replacing in time: a disintegrated flywheel can destroy the bellhousing too. At a clutch replacement the two go together anyway.

The vanes of the variable geometry turbo are glued together by soot and oil arriving through the EGR. First you get overboost or a lack of boost, then loss of power above 2,000 rpm, and finally limp mode. Caught in time it is enough to remove the turbo, clean it and fit a new actuator rod. Short urban trips and gentle, low rev driving speed up the deposits.

The G62 sensor tells the engine control unit how hot the coolant is. If it is faulty, the control unit thinks a warm engine is cold, and runs it rich: hard warm or cold starting, a rough idle, markedly increased fuel consumption, and a dash temperature gauge that jumps around or never reaches its usual reading. The part is cheap and can be replaced in half an hour: the trouble is that many people do not recognise it and replace an injector or a lambda sensor instead. If the fault persists, the rich mixture can destroy the catalytic converter too.