Audi A6

Upper guide rail breaks; chain then runs on the mounting bolt. On the A6 C6 with longitudinal V8 just as laborious as on the S4. Timing chain cover leaks — sealing also requires engine removal. Costs from 4,000 €.

Symptoms: Rattling on cold start, ticking sound at low rpm, engine warning light, limp-home mode

On front-wheel-drive variants of the A6 C6 4.2, the Multitronic gearbox was a known weakness with RPM fluctuations and juddering. Quattro models with Tiptronic are significantly more reliable.

Symptoms: Heavy RPM fluctuations, juddering on acceleration, complete gearbox failure in extreme cases

The four camshaft adjusters on the BAT V8 wear due to inadequate oil supply. Rattling on start, camshaft fault codes and limp-home mode are typical symptoms.

Symptoms: Rattling on start, engine warning light, limp-home mode, power loss at low rpm

FSI-typical carbon deposits on intake valves. Particularly pronounced on the A6 C6 as a company car with lots of short trips. Power loss of up to 40 hp. Only BEDI cleaning helps.

Symptoms: Declining engine power, rough idle, poor throttle response, rough cold start

Elevated oil consumption from valve stem seals and piston rings is widespread on the 4.2 FSI V8. On the A6 with long service intervals, often noticed too late. 1–2 L/1,000 km typical at high age.

Symptoms: Oil level falling between changes, blue haze on cold start or after overrun phases

Water pump on the 4.2 FSI A6 fails after 100,000–140,000 km from bearing wear or defective seals. Simultaneous thermostat replacement recommended. Combination costs 500–1,200 €.

Symptoms: Coolant level falling, temperature gauge rising, heater giving less heat, coolant smell

The FSI high-pressure pump on the BAT fails after 80,000–100,000 km. Starting problems and power loss result. On the A6 C6 the pump is difficult to access due to tight engine bay conditions.

Symptoms: Hard starting, power drop, jerking, fault messages regarding injection quantity

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.