Audi RS4
The BNS is a high-revving V8 with 420 PS at 7,800 rpm and an 8,250 rpm redline — piston speed at rated rpm: 25.4 m/s, identical to a 2012 F1 engine. FSI direct injection without port injection leads to the most aggressive carbon build-up of all 4.2 FSI variants: according to specialist workshops, no RS4 B7 reaches its rated power on the dyno — measured outputs were 347 to 385 PS instead of 420. Mechanical intake cleaning (BEDI) every 15,000–20,000 km restores power, chemical cleaning is not sufficient. Oil cooler connections corrode through galvanic corrosion (aluminium against steel) and are almost always seized at 15+ years of vehicle age. Water-cooled alternator costs four figures to replace. Oil changes every 10,000 km with 5W-40; at high oil consumption use 15W-50. Compression ratio 12.5:1 requires Super Plus fuel.
RS4 Cabrio — V8 sound under open sky, the collector's piece
Same V8, open roof — rarest B7 variant and acoustically the most intense. 420 hp naturally aspirated with no roof: every tunnel run becomes an event. Heavier than the sedan, less rigid, but the sound experience compensates for everything.
Engine Weaknesses 8
The main problem of the BNS: FSI without port injection heavily cokes the intake valves. Specialist workshops measure 347–385 hp instead of the stock 420 hp. Mechanical BEDI cleaning every 15,000–20,000 km needed; chemical cleaning is insufficient.
Symptoms: Gradual power loss over months, rough idle, increased fuel consumption, sluggish throttle response in the upper rev range. Often only measurable on a dyno.
The timing chain sits on the gearbox side. Guide rails and tensioners wear; replacement requires engine-gearbox separation. With consistent oil changes (max. 10,000 km) the chain lasts significantly longer. Cold-start rattling is the warning sign.
Symptoms: Rattling on cold start that disappears after warm-up. At advanced wear, permanent chain rattling and engine warning light.
Four camshaft adjusters wear from oil-deficiency-related abrasion. Oil quality and short change intervals (max. 10,000 km) are critical. Rattling on cold start and fault codes are typical signs.
Symptoms: Rattling on cold start in the camshaft area, power loss at low rpm, engine warning light with camshaft fault codes.
The oil cooler connections (aluminium) suffer from galvanic corrosion with the steel lines. After around 15 years the connections are almost always seized — even weeks of penetrating oil often makes no difference. Oil cooler and both lines must be replaced completely.
Symptoms: Oil weeping at the oil cooler, seized fittings when attempting maintenance, whitish corrosion marks at the oil cooler connections.
The BNS has a water-cooled alternator — unusual and expensive to replace. The combination of water cooling and high thermal load in the engine bay makes this component more failure-prone than conventional alternators.
Symptoms: Battery warning light, charging voltage too low, electrical consumers drop out, coolant loss at the alternator.
The FSI high-pressure pump can fail after 80,000–100,000 km. Without sufficient fuel pressure the engine runs in limp mode with a clear power loss.
Symptoms: Engine stuttering under load, power loss, engine warning light with fuel pressure fault codes, difficult starting.
The DRC system (Dynamic Ride Control) connects the shock absorbers diagonally via hydraulics. When a leak develops, the system loses fluid; complete replacement costs 3,000–5,600 €. Alternative: disable with Bilstein B8 sports dampers, registration-free and cheaper.
Symptoms: Increased body roll in corners, oil traces on the shock absorbers, uneven spring travel, DRC warning in the instrument cluster.
With a sporty driving style and frequent high-revving to 8,000+ rpm, 1 L/1,000 km oil consumption is normal and not a defect. Specialist workshops recommend switching to 15W-50 to reduce oil quantity drawn into the induction system via the crankcase breather.
Symptoms: Falling oil level between services, faint oil smell at high loads. When buying: ask whether the previous owner needed to top up oil.
Vehicle Weaknesses 11
The Dynamic Ride Control hydraulic suspension operating at ~15 bar system pressure is known for leaking dampers. If one damper fails, the others wear faster. Repair requires dealer-level special tooling.
Worn control arms are the most common MOT failure on the S4 B7. Ball joints and track rod ends suffer under the heavy vehicle weight and spirited use.
On quattro models the propshaft centre bearing can cause problems and produce a dull knocking noise, especially when accelerating. Typical wear damage at higher mileage.
Rust forms at the weld points of the rear longitudinal members, in the area between the rear wheel arch and the bumper, due to inadequate cavity sealing. Structurally relevant at high mileage.
The upper front control arms can fail at higher mileage and are expensive to source. Typical wear pattern on sportily driven examples.
The weight of the 4.2-litre V8 combined with the typical spirited driving style leads to above-average wear on brake discs and pads. Maintenance costs are substantial.
Due to the high vehicle weight and strong engine the S4 B7 brake discs and pads wear faster. Frequent disc changes are necessary especially with aggressive driving.
Wheel bearings wear on the RS4 B7 due to the high forces of the quattro drivetrain combined with spirited driving. At high mileage one or more wheel bearings require replacement.
Comfort control modules for the lighting system can fail and require replacement. Affects older vehicles with high mileage in particular.
The plastic gears in the heater flap actuator motor break and cause clicking inside the dashboard. A widespread problem on B6/B7 generation vehicles.
Stone chips on the bonnet and bumper are very common due to the sporty driving style and lowered suspension. Original B7 examples show typical chip damage after years of use.