2004 Audi A6 diesel: common problems and MOT failures

What goes wrong more than usual on a 2004 Audi A6 diesel?

Parts flagged at MOT more often on the 2004 Audi A6 diesel than on all cars registered in 2004.

• Suspension arm bushes and joints2.1× usual
  Audi A6

  19.9% All 2004 cars

  9.3%

  Failed outright at MOT: 4.8%, against 2.1% of all 2004 cars. The rest were advisories or minor defects.

  Rough price £120–£180 (one arm) ClickMechanic

  At the viewing: Listen for clunks over bumps and feel for the steering wandering. Worn arm bushes show as cracked rubber near the wheels.

• Drive shaft (CV) joints2.4× usual
  Audi A6

  15.8% All 2004 cars

  6.6%

  Failed outright at MOT: 7.4%, against 3% of all 2004 cars. The rest were advisories or minor defects.

  Rough price £60–£350 our estimate

  At the viewing: Drive slowly on full steering lock in both directions and listen for clicking. Look for split rubber boots behind the front wheels.

• Anti-roll bar link bushes4.3× usual
  Audi A6

  8.2% All 2004 cars

  1.9%

  Failed outright at MOT: 1.8%, against 0.5% of all 2004 cars. The rest were advisories or minor defects.

  Rough price £100–£280 (pair of drop links) Checkatrade

  At the viewing: Drive slowly over bumps and listen for a knock or rattle from the front. Worn anti-roll bar links are a cheap fix.

• Diesel smoke emissions4.9× usual
  Audi A6

  3.9% All 2004 cars

  0.8%

  Failed outright at MOT: 3%, against 0.7% of all 2004 cars. The rest were advisories or minor defects.

  Rough price £175–£900 (catalytic converter) ClickMechanic

  At the viewing: Look for smoke when revving the warm engine and for engine or DPF warning lights.

• Rear fog light2.1× usual
  Audi A6

  3.2% All 2004 cars

  1.5%

  Failed outright at MOT: 3%, against 1.5% of all 2004 cars. The rest were advisories or minor defects.

  Rough price £10–£80 our estimate

  At the viewing: Ask a friend to check every light while you work the switches: indicators, brake lights, fog lights and reversing lights.

Common 2004 Audi A6 diesel MOT failures and advisories

The share of 2004 Audi A6 diesel MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.

• Suspension
  49% of testsRough price £120–£400

  At the viewing: Listen for knocks over speed bumps, and look behind each front wheel for a snapped coil spring.

• Brakes
  40% of testsRough price £150–£350

  At the viewing: Look for a lip on the disc edges and feel for judder or pulling when braking firmly from about 40mph.

• Lights and electrics
  39% of testsRough price £10–£80

  At the viewing: Ask a friend to check every light, including brake lights and indicators, while you operate them.

• Tyres
  32% of testsRough price £70–£150

  At the viewing: Check the tread on all four tyres, including the inside edges, and look for cracks or bulges.

• Oil and fluid leaks
  18% of testsRough price £80–£600

  At the viewing: Look under the engine and on the ground where the car is usually parked for fresh oil or fluid.

• Driveshafts and joints
  16% of testsRough price £60–£350

  At the viewing: On full steering lock, drive slowly and listen for clicking from the front wheels.

Known faults on the 2004 Audi A6 diesel

Reported by owners, mechanics and buying guides for this model and age. Check which engine the car has, as some apply to one engine only.

• Electrical gremlins

  All engines

  Electrical faults hit almost 40% of cars, and the engine ECU can fail, shown by warning lights or a sudden loss of power.

  At the viewing: Check every warning light goes out and test all the electrics.

  Source: What Car?: Audi A6 (2004-2011) reliability

• Air conditioning faults

  All engines

  Around a quarter of cars have air con faults.

  At the viewing: Make sure it blows icy cold with no damp or musty smell.

  Source: What Car?: Audi A6 (2004-2011) reliability

• Oil use (diesel)

  Diesel

  The diesels can use oil between services.

  At the viewing: Check the oil level and ask how often it needs topping up.

  Source: What Car?: Audi A6 (2004-2011) reliability

Questions to ask the seller before buying a 2004 Audi A6 diesel

Ask before you travel to see it. A seller who knows the car will have answers, and receipts.

1. Any recent work on the suspension arm bushes and joints? (Flagged at MOT 2.1× as often on the 2004 Audi A6 diesel as on other cars the same age.)
2. Any recent work on the drive shaft (cv) joints? (Flagged at MOT 2.4× as often on the 2004 Audi A6 diesel as on other cars the same age.)
3. Any recent work on the anti-roll bar link bushes? (Flagged at MOT 4.3× as often on the 2004 Audi A6 diesel as on other cars the same age.)
4. Can I see the service history and receipts for any big jobs?