The B6 S4 was the first Audi S4 with the 4.2-litre V8, replacing the biturbo 2.7 of the B5. The BBK engine produces 344 hp and revs to 7,200 rpm through multi-point port injection, paired exclusively with quattro all-wheel drive and either a 6-speed manual or ZF 6HP19 Tiptronic automatic. It remains one of the more characterful performance sedans of its era, though its reputation is heavily shaped by the timing chain and tensioner service, which requires engine removal and runs into thousands of euros.
Charismatic naturally aspirated V8
Port injection avoids carbon buildup
Timing chain service requires engine out
Excessive oil consumption widely reported
Buy if: You want a characterful V8 Audi and can find one with documented timing chain service or have the budget for preventive replacement.
Avoid if: You cannot set aside a substantial budget for major engine work, or the car has cold-start rattle and no maintenance records.
Expected Annual Maintenance Costs
Common Problems
Plastic guides and tensioners wear out, causing chain rattle and potential engine damage · more· less
The BBK 4.2 V8 has its timing chain system at the rear of the engine, facing the firewall, meaning the entire engine must be removed for service. The plastic chain guides crack and break, tensioners lose pressure, and chains stretch over time. Early symptoms include a rattle on cold start lasting a few seconds, progressing to persistent rattle and eventually camshaft correlation fault codes (P0016/P0017). B6 models (2003-2005) are more prone to failure than later B7s, which received revised components from 2006 production onward. Failures have been documented as early as 60,000 km, though many engines reach 150,000 km without issues. Parts kits cost around €800-1,200, but the 25-30 hours of labor (engine out, timing service, reinstall) drives the total to €3,500-6,000 at a specialist. Audi dealers have quoted significantly more. Preventive service is recommended by most specialists before 120,000 km regardless of symptoms.
Many engines consume 0.5-1.0 litre per 1,000 km, with some far worse · more· less
Oil consumption is widely reported on B6 S4 engines, with Audi at one point stating that 1 litre per 1,000 km was within specification. Common causes include worn valve stem seals (the most frequent culprit), weak PCV system allowing crankcase pressure to push oil into the intake, and worn piston rings on higher-mileage engines. Topping up oil regularly (€200-400/year in oil costs) is manageable, but if consumption exceeds 1 litre per 1,000 km, the underlying cause should be diagnosed. Valve stem seal replacement costs around €1,500-2,500 (labor-intensive but does not require engine removal). A full engine rebuild for piston rings or scored cylinders can reach €4,000 or more. Regular oil changes with quality synthetic oil at 7,500-10,000 km intervals help manage consumption.
Multi-link front suspension has 8 control arms with bushings that wear by 80,000-120,000 km · more· less
The B6 platform uses a multi-link front suspension with 4 control arms per side (8 total). The bushings, particularly the upper arms, are known to wear prematurely, causing clunking over bumps, imprecise steering, and uneven tire wear. A TSB exists for the upper arm bushings, which can crack or allow the metal spacer to unbond from the rubber. Audi designs these arms so the bushings cannot be replaced separately. A full set of 8 aftermarket control arms with hardware costs around €400-600, with labor of €400-600 for the complete front end. OEM arms are significantly more expensive. Alignment is required after replacement. On a car of this age, expect to replace the full set at least once during ownership if it has not already been done.
Gaskets harden with age and heat, causing oil leaks around both V8 valve covers · more· less
The valve cover gaskets on the 4.2 V8 harden and shrink over time, leading to oil seepage and eventually dripping onto the exhaust manifolds, which can cause burning oil smell and smoke. Both sides (16 cam end plug seals and 8 spark plug tube seals total) typically need attention at the same time. The valve covers themselves can warp on higher-mileage engines, requiring resurfacing or replacement. Parts for a complete gasket kit cost around €100-150. Labor runs €300-750 depending on the shop, as intake manifold removal is needed for access on one bank. This is considered routine maintenance on a V8 of this age.
Side-mounted auxiliary radiators develop leaks at plastic fittings and hose connections · more· less
The B6 S4 has two auxiliary radiators mounted in the front fender area that supplement the main radiator for the V8's cooling needs. These are prone to developing leaks at the plastic end fittings and hose connections, particularly as they age. Symptoms include coolant loss visible at the lower front edges of the wheel wells. The radiators themselves are relatively inexpensive (€80-120 each), but some aftermarket replacements have poor quality end caps that fail within months. OEM or quality aftermarket units are recommended. If a thermostat has previously seized, the resulting overpressure can accelerate auxiliary radiator failure. Labor is moderate as the components are reasonably accessible.
Coil packs fail individually, causing misfires on affected cylinders · more· less
The BBK V8 uses 8 individual coil-on-plug ignition coils. These are a known wear item across many VAG engines and can fail at any mileage. Symptoms include rough idle, misfires on specific cylinders, and a flashing check engine light. Individual coils cost €20-40 each, and most specialists recommend replacing all 8 along with spark plugs when one fails, bringing the total to €200-500 including labor. Spark plugs should be changed every 40,000-60,000 km as part of regular maintenance. This is a relatively minor issue that is easy and inexpensive to diagnose and fix.
High-maintenance V8 that rewards proactive owners
The B6 S4's 4.2 V8 is a characterful engine, but ownership demands a proactive approach to maintenance. The timing chain service dominates the cost picture and should be considered a when-not-if expense on any car that has not already had it done. Oil consumption, control arm wear, and coolant system maintenance add to the running costs. Cars with documented timing chain service and consistent maintenance history are significantly lower-risk purchases than those with unknown histories.
Recalls and Technical Service Bulletins
Headlight switch wiring harness short circuit risk (2004 models, knee bolster area)
Verify completed
Takata passenger airbag inflator replacement (2005 models, inflator degradation risk)
Critical - verify completed
Contact Audi with the VIN to verify all recalls and service campaigns have been completed. The Takata airbag recall is particularly important as the inflator can rupture on deployment.
Warranty Status
Factory warranty (2 years)
Expired on all B6 S4 models
Rust perforation warranty (12 years)
Expired on all B6 S4 models
All B6 S4 models are well outside both their original 2-year factory warranty and 12-year rust perforation warranty. No manufacturer extended warranty programs are available for these vehicles. Third-party warranties are available but typically exclude timing chain and pre-existing oil consumption issues.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.