Audi S4
Supercharged V6 with 245 kW in the S4/S5 B8. Proven drivetrain with linear power delivery. Supercharger belt and water pump are known service items.
Supercharged V6 replaces V8 — faster, more reliable, less soul
The 3.0 TFSI supercharged V6 replaces the NA V8. Faster? Yes. More reliable? Significantly. More boring? Also yes. The supercharger whine has its own charm, but the sound doesn't touch the predecessor's high-revving V8. With the ZF eight-speed, one of Audi's most reliable powertrains.
Engine Weaknesses 15
The intercooler integrated into the Eaton supercharger can develop leaks from thermal stress. Coolant enters the combustion chamber and can cause a hydrolock with total engine damage.
Symptoms: Coolant loss without visible external leak, misfires on cylinder 3, white exhaust smoke, power loss.
Rare but catastrophic: if the high-pressure pump fails, metal swarf is distributed throughout the entire fuel system. All lines, injectors and the tank must be flushed or replaced.
Symptoms: Engine will no longer start, engine warning light with fault code 'rail pressure too low', rough running, sudden power loss.
Hydraulic chain tensioners lose oil pressure overnight. On cold start the chain rattles for 1–3 seconds until pressure builds. Persistent rattling indicates a stretched chain or defective tensioners.
Symptoms: Metallic rattling on cold start (1–3 seconds), disappears once warm. With advanced wear also persistent rattling and engine warning light.
Particularly models from 2010–2012 have water pumps with plastic impellers that wear prematurely. Coolant loss and overheating can follow. Replacement requires removal of the supercharger.
Symptoms: Coolant warning, falling coolant level, coolant puddle under the vehicle, rising temperature gauge.
The drive shaft bearing on the Roots supercharger wears at high mileages. Play in the drive shaft is detectable by hand. A complete supercharger replacement is usually necessary.
Symptoms: Mid-range whistling or grinding in sync with engine rpm, metallic noise from the supercharger, increasingly louder.
The upper chain tensioners lose oil pressure at standstill; the timing chain rattles for 1–2 seconds on cold start. With ongoing symptoms, guide rail damage and in the worst case chain jump threatens.
Symptoms: Metallic rattling immediately after cold start, fades after 1–2 seconds. With advanced wear, permanent chain noise.
The 3.0 TFSI CAKA uses an Alusil cylinder bore. When the coating wears or is damaged, oil consumption rises progressively. A defective crankcase ventilation makes the problem worse.
Symptoms: Oil consumption above 0.5 L/1,000 km, blue exhaust smoke under load, oil smell in the cabin.
The 3.0 TFSI S4/S5 shows failures of the coolant pump and thermostat at higher mileage. Thermostat faults lead to incorrect operating temperature; pump failures carry overheating risk.
Symptoms: Temperature fluctuations on the cockpit display, coolant loss, engine reaches operating temperature too late or overheats.
The front bearing of the Eaton supercharger (nose bearing) can wear at high mileage and cause whistling noises. In extreme cases, bearing failure leads to supercharger damage.
Symptoms: Whistling or whining from the supercharger area, especially at low rpm or at idle, getting louder at higher rpm.
On CGW engines (CGWA/CGWB/CGXB) blanking screws were fitted instead of check valves (part no. 06E 103 271 A) in the oil passage. Oil drains into the sump; chain rattles earlier than normal on start.
Symptoms: Loud chain rattling on cold start that develops faster than normal, oil pressure loss at standstill.
The PCV membrane tears at 60,000–80,000 km, creating excessive vacuum in the crankcase. Oil is drawn into the intake system. Its position under the supercharger makes repair expensive.
Symptoms: Rough running, power loss, engine will not rev beyond 4,000 rpm, increased oil consumption, white smoke.
Direct injection without port spray leads to carbon deposits on the intake valves from around 70,000 km. Walnut blasting is needed to restore full power.
Symptoms: Cold-start misfires, hesitant throttle response, worse fuel pick-up, increased fuel consumption.
The Eaton supercharger drive belt must be changed every 60,000 km according to Audi (internally revised from 90,000 km). A broken belt causes boost loss and supercharger damage.
Symptoms: Whistling or squealing from the engine bay, power loss at higher rpm; rarely: engine warning light.
As a direct-injection engine the 3.0 TFSI does not wet the intake valves with fuel, so oil mist from the crankcase breather deposits as oil carbon. Results in power loss and jerking.
Symptoms: Jerking at part throttle, starting problems on cold engine, power loss, rough idle.
Ignition coils and spark plugs on the 3.0 TFSI wear at 60,000–80,000 km. Mixed misfires and engine judder follow. Regular replacement prevents catalyst-damaging misfires.
Symptoms: Engine judder, rough running under load, engine warning light (P0300–P0306), noticeable power reduction.
Vehicle Weaknesses 14
The 7-speed dual-clutch gearbox DL501 is prone to mechatronics failures. Typical: judder on pull-away, delayed gear changes or complete failure. Repair costs €3,000–5,000, a new unit up to €11,000.
At higher mileage, wishbone rubber bushes and ball joints wear out. Typical creaking when driving over uneven surfaces. A complete wishbone set including fitting costs €1,200–1,500.
The optional adaptive suspension is prone to damper failures from around 120,000 km. Affected dampers fail when hot. A single adaptive damper costs €500 net; a complete front replacement around €2,200.
On the optional sport differential, grease/oil leaks from the propshaft. Cause: the end-cap bonding fails to hold the internal pressure (TPI 2025572/1). Repair requires gearbox removal.
The rear subframe and axle carriers rust under the plastic covers where dirt and moisture accumulate. Severely affected carriers require replacement.
MMI system fails — screen black, no audio or permanent reboot loops. Cause is often water damage to the Bluetooth control unit in the footwell or overvoltage during a battery change.
On the optional panoramic roof, the drain spouts in the wheel arches become blocked or detach. Water runs into the interior rather than away — headlining and rear wheel arch get wet.
The AC compressor on the B8 has no magnetic clutch and is electronically regulated. With increasing mileage the control unit or the compressor itself fails — frequently after 100,000–150,000 km.
Control units (including Bluetooth module, interior surveillance, hands-free phone kit) fail to enter sleep mode properly and create excessive quiescent current draw. Battery flat after short periods of standing.
Rust forms on the wheel arch edges of front and rear wings. Inadequate factory cavity protection promotes corrosion — on early models Audi replaced wings under goodwill.
The large brakes on the S4 B8 wear quickly under spirited driving. A complete front-and-rear brake disc set in OEM quality costs around €1,400.
From build year 2008, door seals detach from the adhesive in places — a well-known early issue on the B8. Moisture ingress increases and wind noise worsens. Audi replaced seals under goodwill on early cars.
The xenon ballast in the headlight fails due to moisture ingress or ageing. Affects the standard Bi-Xenon headlights — one headlight sporadically goes out or flickers.
The universal joint in the steering column or the electric power steering pump produces clicking or grinding noises during slow steering inputs and manoeuvring. Particularly noticeable during temperature swings.