Audi A6

On the 2.8 FSI BDX, the timing chain sits on the transmission side — replacement requires engine removal. Typical cost is €3,000–4,500. Chain stretch occurs from around 150,000 km, often accelerated by infrequent oil changes.

Symptoms: Clattering noise at cold start, power loss, fault code for camshaft position, engine hesitation

The 2.8 FSI shows elevated oil consumption due to piston ring wear or faulty valve stem seals. Audi had quality issues with cylinder bore honing on some of these engines. Engine rebuild costs €2,100–4,100.

Symptoms: Significantly elevated oil consumption, compression differences between cylinders, power loss, occasional blue smoke

The BDX 3.2 FSI, like all 3.2 FSI V6 engines, is prone to piston slap from piston/cylinder wear. Leads to knocking noises and high oil consumption. Expensive repair often not economically viable.

Symptoms: Knocking noise from the engine under load, elevated oil consumption, power loss

The timing chain on the BDX 3.2 FSI can stretch. If the chain skips teeth, engine damage is likely. Rattling at cold start is the first sign. Chain replacement is labour-intensive and expensive.

Symptoms: Cold-start rattling that subsides when warm. Rough running when stretch is severe.

Direct injection (FSI) does not clean the intake valves. Oil mist from crankcase ventilation builds up deposits on the valves. Tank additives do not help — only mechanical cleaning (walnut blasting) is effective.

Symptoms: Juddering at cold start, power loss especially at low rpm, increased fuel consumption, rough idle

The continuously variable Multitronic gearbox (01J/0AW) is considered the most serious weakness. Judder, rev fluctuations and complete failure. Early build years up to 2007 are particularly badly affected.

The A6 Allroad with adaptive air suspension frequently suffers from defective air spring bellows and overloaded compressors. Leaking bellows force the compressor to run continuously until it fails.

Blocked drain channels under the battery and sunroof allow water to enter the cabin. The comfort control module in the driver's footwell is damaged, leading to MMI total failure.

The Allroad with air suspension suffers from defective compressors and leaking air bellows. A leaking air bellows causes the compressor to run continuously until it overheats.

The Multitronic CVT tends to judder when pulling away, rpm fluctuations at partial load and, in the worst case, complete failure. All front-wheel-drive models are affected.

The high vehicle weight (up to two tonnes) accelerates wear of control arms, joints and anti-roll bar bushes. From around 150,000 km, extensive suspension work is virtually unavoidable.

Older A6 C6 examples show corrosion starting at the sills, door sill lower edges and tailgate. Where paint is damaged in the underbody area, corrosion progresses rapidly.

The cast-aluminium front control arms are prone to rubber bush wear. The long steel bolts in the wheel carrier corrode particularly badly and become extremely difficult to remove.

Pre-facelift vehicles (up to 2001) in particular show rust at the front wheel arches, door sill lower edges, and on the Avant at the roof edge above the windscreen.

Blocked drain holes under the battery lead to water ingress into the interior and can damage control units. Leaking cabin air filter housing seals exacerbate the problem.

The shaft seal between gearbox and propshaft on the A6 C5 eventually loses its seal. Gearbox oil drips onto the catalytic converter and burns off there. Often only diagnosed by smell or visual inspection from underneath.