Audi S4 B7

This is the most critical and expensive issue on the B7 S4. The 4.2L V8 uses timing chains located at the rear of the engine against the firewall, meaning the engine or subframe must be lowered for access. The plastic chain guides deteriorate in the high-heat, high-vibration environment, and the hydraulic tensioners lose pressure over time. Symptoms start with a brief rattle on cold startup (the so-called death rattle) that progressively worsens. If the guides disintegrate or the chain skips, catastrophic valve damage can result. Failures have been reported from as early as 60,000 km, though most occur between 100,000 and 160,000 km. Parts for a complete timing chain service kit cost approximately €800-1,400 for OEM components. Labor is typically 16-25 hours because of rear-engine access requirements, pushing total cost to €3,500-6,000 at a specialist. Audi dealers can charge more. Frequent oil changes with quality oil help slow guide wear, but preventive replacement is the only reliable solution. When buying, always ask whether this service has been completed.

The 4.2L V8 in the B7 S4 is prone to elevated oil consumption, and Audi historically considered up to 1 litre per 1,000 km to be within specification. The primary cause is hardened and cracked valve stem seals, which allow oil to leak past the valve guides and into the combustion chambers. The engine bay is tightly packed, causing the V8 to run hotter than in larger Audi models, which accelerates seal degradation. Mild cases (1 litre per 2,000-3,000 km) can be managed by topping up oil regularly. Severe cases require valve seal replacement, which involves significant engine disassembly and costs €3,000-4,000 at a specialist. A PCV valve failure can also contribute to oil consumption; replacing the PCV system costs approximately €300-500 and should be checked first as a less expensive cause. Blue smoke on startup or under hard acceleration indicates oil burning.

The B7 S4 shares the multi-link front suspension with the B7 A4, featuring 4 control arms per side (8 total). The rubber bushings and ball joints are known to wear relatively quickly, typically between 80,000 and 120,000 km. Worn bushings cause clunking over bumps, vague steering feel, uneven tire wear, and can lead to MOT/TUV failure. Audi issued a TSB for the upper control arm bushings, which can crack or have the metal spacer unbond from the rubber. A complete front control arm kit with all 8 arms, bushings, and hardware costs €300-600 for aftermarket parts or €600-1,000 for OEM. Labor to replace all 8 arms typically runs €400-800 at an independent specialist. Most B7 S4s at this age will need at least one set of control arms during ownership.

The 4.2 V8 has 8 ignition coil packs, one per cylinder, and they are prone to failure from heat exposure. Symptoms include engine misfires, rough idle, and individual cylinder misfire codes (P0300-P0308). Coil failures typically begin around 60,000-80,000 km, and once one fails, others often follow within the next 20,000 km. Individual OEM coils cost approximately €20-35 each. It is common practice to replace all 8 simultaneously along with spark plugs, bringing the total to €200-500 including labor. This is a straightforward and inexpensive repair relative to other V8 issues, but ignoring misfires can damage the catalytic converters.

The cooling system on the 4.2 V8 uses several plastic connectors, T-pieces, and elbows that become brittle with age and heat cycling. The upper radiator hose elbow on the passenger side is particularly prone to snapping. When a connector fails, coolant leaks out and the engine can overheat quickly. Individual connectors are inexpensive (€10-30 each), but the labor can be significant depending on location, and it is advisable to replace all accessible plastic coolant components at once. Total cost for a comprehensive coolant system refresh including hoses and connectors typically runs €400-800 at a specialist. Aftermarket aluminium replacement connectors are available for the most failure-prone locations.

The V8 has two valve covers (one per bank) and both gaskets are prone to hardening and leaking as the engine ages. Oil seeps onto the exhaust manifolds, producing a distinct burning smell and visible smoke from the engine bay. This is a common issue on virtually all high-mileage B7 S4s. Parts cost €50-100 for both gaskets. Labor is moderate but requires removing the intake manifold for access to one side, which adds complexity. Total repair cost is typically €400-600 at an independent shop or €700-1,000 at an Audi dealer.

This issue only affects manual gearbox cars. The dual mass flywheel absorbs driveline vibration but the internal springs can weaken and break over time, particularly on cars driven aggressively or with aftermarket tunes. Symptoms include a rattling or chattering noise from the bellhousing area, especially at idle and low RPM. The flywheel costs approximately €400-600 for an OEM part, with aftermarket options available. Labor requires gearbox removal (6-8 hours), so replacing the clutch at the same time is recommended. Total cost for DMF and clutch replacement is typically €1,200-1,500 at an independent specialist. Tiptronic automatic cars do not have this issue.

The ZF 6HP19 Tiptronic automatic is generally robust but requires regular fluid and filter changes that many owners neglect. When the internal solenoids degrade or the mechatronic seal between the controller and case fails, symptoms include delayed gear engagement, harsh or jerky shifts, and eventually limp mode. Solenoids should ideally be replaced around 150,000 km. A transmission fluid and filter service costs €200-300 and should be done every 60,000 km. Solenoid replacement costs €800-1,200, while a full mechatronic unit repair can reach €2,000-2,500. ZF introduced updated green ATF (G060162A2) that helps prevent some of these issues. Manual gearbox cars are not affected.