Audi S4 B7

The timing chain itself rarely fails - it's the plastic guides, tensioners, and cam adjusters that wear out or break. Mean average failure occurs around 100,000 km, though some fail as early as 60,000 km and others survive past 150,000 km. Symptoms include rattle on cold start (1-2 seconds is normal, more than 5 seconds is concerning). Poor oil maintenance accelerates failure. The timing chains are located at the REAR of the engine facing the firewall, requiring complete engine removal for service. When tensioners fail completely, broken guide pieces can wedge between chain and sprocket causing it to jump - this leads to piston-valve contact and catastrophic engine damage requiring full rebuild. Preventive replacement at 80,000-100,000 km is strongly recommended. Parts cost €2,000-3,000, labor adds another €3,000-5,000 due to engine removal. RS4 with FSI direct injection doesn't suffer this issue.

Manual transmission models use a dual mass flywheel to smooth out vibrations from the V8. The DMF has internal springs that wear over time, typically becoming audible around 100,000-120,000 km. First symptom is a rattling sound on cold start that goes away when you press the clutch. As it worsens, you'll hear rattling during gear changes and when releasing the clutch. Replace immediately once rattling starts - a failed DMF can damage the clutch and transmission. Labor is significant (6.5-7.5 hours) due to Quattro drivetrain. When replacing, always do clutch at the same time. OEM parts (LUK) cost €400-600 for DMF + clutch kit. Independent specialists charge €1,200-1,500 total, Audi dealers €2,000-2,500. The Quattro system adds complexity and cost compared to FWD models.

The 4.2L V8 burns some oil even when healthy - checking and topping up between services is normal. However, excessive consumption (>1L per 1,000 km) with blue smoke puffs on cold start indicates worn valve stem seals. Oil pools around valve stems when engine is off, then burns on startup. Spark plugs show heavy carbon buildup. Most noticeable after car sits overnight. Typically appears after 80,000-120,000 km. A compression test rules out other causes - good compression confirms it's valve stem seals. Repair requires pulling camshafts (which means chain sprockets come off) but can be done without removing cylinder heads. JHM head gasket kit includes all 40 valve stem seals plus gaskets and bolts. Many mechanics prefer removing heads for better access, adding to cost. Independent specialists: €2,000-2,500, dealers: €3,000-4,000. Some owners opt to simply monitor oil and top up, living with blue smoke rather than expensive repair.

B7 S4 uses a sophisticated multi-link suspension with small ball joints that are its weak point. Bushings typically worn by 70,000 km, definitely need attention by 100,000-120,000 km. Symptoms: clunking over bumps (especially while turning), steering play/vagueness, squeaking on uneven surfaces. If severely worn, tire wear becomes uneven and car may pull to one side. Independent specialists recommend replacing entire control arms rather than pressing in new bushings - the ball joints get sticky after 10+ years and pressing can damage arms. Front suspension has 4 arms that commonly need replacement. OEM/Genuine parts recommended (Lemförder, Meyle HD). DIY with quality parts: €400-600. Independent shop: €800-1,200. All four corners at dealer: €2,000-2,500. Upgraded options available from 034 Motorsport with density line bushings for firmer ride.

B6/B7 S4 has auxiliary radiators on both sides that are notorious for leaks. Each costs just over €100 and is DIY-friendly. Common leak point is where coolant temp sensor mounts - rubber O-ring fails. Also check metal coolant pipes that run under intake manifold (part 079121481G with N90806302 O-ring). Look for pink crystals under manifold - telltale sign of coolant leak. Another issue is silver pipe running front of oil pan - held by one bolt with washer and O-ring seal that deteriorates. Thermostat failure is also common, causing either overcooling (stuck open, poor heater performance) or overheating (stuck closed). Thermostat alone: €400-600 parts + €400-600 labor. The whole cooling system uses plastic components that become brittle with age and heat cycles. Always flush entire system thoroughly when replacing water pump - old coolant degrades seals prematurely. Budget €600-1,000 for addressing cooling system issues at independent shop.

One of the most common B6/B7 S4 issues. Symptoms: check engine light with misfire codes, flashing CEL, rough idle, loss of power. V8 has 8 coil packs, one per cylinder. When one fails, that cylinder stops firing. Diagnosis is easy: swap suspected coil to another cylinder - if misfire follows the coil, it's bad. OEM coils cost about €45 each from ECS Tuning or FCP Euro. This is a 5-minute DIY job - coils mounted on top of engine, easily accessible. Many owners replace all 8 preventively with spark plugs at 80,000-100,000 km. All 8 coils + 8 spark plugs: €400-600 parts + labor if not DIY. Dealers charge €480+ but it's unnecessary - parts are cheap and installation is simple. Failing coils allow unburned fuel into exhaust, potentially damaging catalytic converter (€1,500-2,500 to replace), so fix immediately. Keep spare coil in boot - they fail without warning and car runs poorly on 7 cylinders.

Common problem on Audi models after 80,000-100,000 km. Driver's door usually fails first due to most frequent use. Symptoms: grinding noise when operating window, window moves slowly or gets stuck, window only goes up/down partially. Typically it's the regulator (cable mechanism) not the motor - if you hear motor clicking, motor is fine. Cables become frayed and binding restricts movement. Cables are integral to regulator assembly and cannot be replaced separately - entire regulator must be changed. Using OEM or quality aftermarket parts important - cheap regulators fail prematurely. Not particularly complex repair but requires door panel removal and careful reassembly to prevent rattles. OEM regulator: €150-250. Labor: 1-1.5 hours. Total at independent shop: €300-450 per window. If only one-touch auto up/down stops working (but manual operation works), it's usually the window switch (€50-100) not regulator. Can reset one-touch: fully open window, hold button 10 seconds, then fully close and hold button 10 seconds.