Audi RS4
Facelift version of the 2.9 TFSI V6 BiTurbo with OPF and 48V mild hybrid — 450 PS like the DECA, but with particulate filter and BSG starter-generator. The OPF noticeably mutes the V6 sound; the mild hybrid delivers brief boost pulses during launch. The rocker arm bearing issues of the DECA also affect the DNXB — same design, same wear pattern on the exhaust camshaft rocker arm bearing. The water pump is a known weak point as with the DECA. Compared to the DECA: less emotional, but slightly more economical in everyday use through regeneration and coasting.
BiTurbo V6 replaces V8 — faster, wider, less soul
450 hp twin-turbo V6 replaces the NA V8. 0-60 in 4.1 seconds, wider than its predecessor, technically superior. But the sound doesn't touch the B7, and the auto-only gearbox leaves no room for manual nostalgia. The RS4 for people who rank lap times above goosebumps.
Engine Weaknesses 6
Design flaw: water pump leaks internally and draws coolant into the vacuum system. Can cause severe engine damage if not stopped immediately. Improved 6-bolt version available as replacement.
Symptoms: Coolant loss in expansion tank, fault codes P0299, drive interruption message, coolant deposits on engine block bank 1
Small bearing rollers on the rocker arms detach on early units (GP0-P code) and fall into the sump. Caught early, replacement costs a few thousand euros; undetected, total engine failure.
Symptoms: Ticking or knocking on cold start and at idle, engine warning light, metallic noise from cylinder head area
Two turbos in the V6 are exposed to severe heat. Insufficient warm-up and immediate shutdown after full load substantially accelerates bearing wear.
Symptoms: Whistling from turbo area, smoke from engine bay, power drop, increased oil consumption, blue smoke
The 2.9 TFSI V6 BiTurbo uses a cooled indirect charge-air system. Oil supply to both turbos is critical on cold start. Insufficient cool-down after hard use can damage turbo bearings.
Symptoms: Whirring after engine shutdown, smoke from exhaust on cold start after hard use
S-Tronic (PDK) on the RS4/RS5 B9 shows accelerated clutch wear with frequent track/sport use and launch control. Stop-and-go city driving makes it worse.
Symptoms: Juddering on pull-away, dual-clutch noises, gearbox control faults
Turbo direct-injection without port spray. Deposits build on intake valves with frequent short trips or skipped cleaning intervals.
Symptoms: Power loss under partial throttle, rough idle, increased fuel consumption, sluggish throttle response
Vehicle Weaknesses 20
Recall 42L1/42L5: Stress corrosion cracking in the rear trailing arm can increase play. Affected: build years 2019–2021. Missing wheel alignment after the initial recall caused severe rear tyre wear.
Recall 74E3 for S4 B9 (build years 2018–2020): a seat heater wiring fault can cause an occupancy sensor error and deactivate the front passenger airbag.
The optional Dynamic Ride Control suspension on the RS4 B9 tends to develop leaking dampers after several years. Full system replacement including lines costs €5,000–5,500 at a dealer. Service cycle every 6 years recommended.
On some 2019–2021 model years stress corrosion cracking can cause increased play between the trailing arm and wheel carrier, affecting driving stability and causing heavy tyre wear.
The Virtual Cockpit freezes or shows only the speedometer and tachometer during driving. The problem recurs even after software updates. A full digital cockpit replacement is expensive.
At higher mileages, worn wheel bearings and failed ball joints are documented. MOT testers regularly flag suspension geometry faults. Repair including wheel alignment costs around €800–1,500.
The optional electronically controlled suspension shows sporadic fault messages and damper failures. A single adaptive damper costs €500 net and upwards.
The S4 B9 TDI suffers from a software-related hesitation on pull-away: the engine revs to 2,000–2,500 rpm with no forward movement, then power arrives abruptly. Caused by WLTP gearbox calibration. Reduced in Dynamic mode.
The B9 develops coolant leaks from flanges in the cooling circuit. Plastic weld seams can crack — in severe cases overheating is a risk.
On the S4 B9 TDI, AdBlue injector nozzles can block through crystallisation or the urea pump can fail. After a fault message, a countdown to engine lock-out begins.
RS4 B9 brake discs can develop cracks under frequent spirited use, not classified as normal wear. Owner reports of squealing are very common without ceramic brakes.
The optional sport differential requires an oil change every 30,000 km — something many dealers and owners are unaware of. Neglect leads to wear and costly failure.
The S4 B9 shows increased brake disc wear during spirited driving. A complete front-and-rear set in OEM quality costs around €900–2,750.
The MMI system frequently has problems with Bluetooth, CarPlay and online connectivity. A software update is often sufficient, but occasionally a control unit swap is needed.
The ZF 8HP torque-converter automatic shows delayed shifting and judder on pull-away when cold. Audi sometimes describes this as 'state of the art'. A gearbox oil change can help.
On the optional panoramic roof, water drain channels can block or hoses detach, allowing water into the footwell or down the A-pillar.
The optional B&O premium sound system is prone to sporadic audio cut-outs due to control unit software errors. Voltage drops in cold conditions can crash the chip.
Rear wheel bearings on the S4 B9 can wear prematurely — accelerated by spirited driving and the quattro all-wheel-drive system. Cases documented below 80,000 km.
The automatic headlight levelling system shows malfunctions on model years up to 2019 that were never fully resolved. Control module or sensor requires replacement.
Annoying creaks and rattles in the dashboard and door panel area, sometimes occurring after only a short time. Workshop visits often provide no lasting fix.