KNOWN FAULTS · Audi

Audi A6 (C5) 2.5 TDI V6 common problems.

2000–2004 · Diesel

Sources are not verified in real time and no entry confirms that your car is affected.

3 known faults with sources

Applies if: Only if fitted with the automatic gearbox described in the record.

Audi Multitronic (CVT) gearboxAutomatic gearbox

Engine / equipment: Multitronic continuously variable gearbox (01J and successors) in front-wheel-drive Audis: A4 B6/B7/B8, A5 8T and A6 C5/C6/C7
Period mentioned: 2000–2014
Symptoms: Judder or vibration when pulling away (especially uphill), a slipping feeling at low revs, jerky acceleration and limp mode with limited speed; sometimes a burning smell.
Possible cause described: Known failures of the variator chain and pulleys, the hydraulic and electronic control unit and the clutch pack. Audi issued service bulletins, and forums report failures even with the recommended fluid changes, although poor maintenance speeds them up.
Check for the garage: Read the gearbox codes with Audi-compatible equipment, check the fluid change history and, at a specialist, judge whether fluid and a clutch adaptation are enough or the control unit or variator needs repair. With limp mode or a burning smell, stop driving.
Cost cited in the source: A UK specialist says a judder checked early usually costs a few hundred pounds, while ignoring it can end in a full rebuild.A rough figure from the original database, not an up-to-date quote.

Worn camshafts, air mass meter and injection pump on the 2.5 TDI V6Engine

Engine / equipment: 2.5 TDI V6 with distributor pump: Audi A4 (B5 and B6), A6 (C5) and VW Passat B5
Period mentioned: 1997–2005
Symptoms: An engine that runs rough, loss of power or hesitation; now and then the injection pump fails; oil leaks from the engine or gearbox.
Possible cause described: AUTO BILD (March 2008) reports more and more complaints about the A4's 2.5 V6 because of worn camshafts (Audi did not issue a recall) and adds that the Multitronic gearbox fails mainly with this engine, because of its high torque. On the A6 (1997–2004), AUTO BILD lists faulty air mass meters causing loss of power or hesitation, injection pumps that fail now and then and oil leaks from the engine and gearbox, mainly on the TDI. The Passat B5 has the same engine.
Check for the garage: If the engine gets noisier or runs worse with the miles, have the garage check the camshafts by removing the cam covers. Read the codes and test the air mass meter before touching the pump. With the Multitronic gearbox, ask for its history and check that it does not jerk or slip.
Cost cited in the source: No verified estimate; ask the garage for a quote.A rough figure from the original database, not an up-to-date quote.

Applies if: All versions; AUTO BILD lists the immobiliser among the most frequent electrical faults.

Will not start because of the immobiliser on the Audi A4 (B6) and A6 (C5)Electrical and electronic systems

Engine / equipment: Audi A4 2000–2004 (B6) and A6 1997–2004 (C5), all versions
Period mentioned: 1997–2004
Symptoms: The car will not start because the immobiliser blocks it. On the A6 the central locking, windows and battery also often fail.
Possible cause described: AUTO BILD says that on the 2000–2004 A4 a faulty immobiliser often prevents starting, and that the repair is a new instrument cluster (which houses the immobiliser), for about €500. On the 1997–2004 A6 it lists the immobiliser, central locking and window regulators among the main culprits for electrical faults, plus a battery that often fails.
Check for the garage: First test the battery: with low voltage the immobiliser fails too. Try the spare key. If it still will not start with either key, the garage diagnoses the immobiliser in the cluster with Audi equipment before replacing the cluster, because the keys have to be matched.
Cost cited in the source: About €500 for the instrument cluster (AUTO BILD, 2008).A rough figure from the original database, not an up-to-date quote.