The 2017 S4 (B9 chassis) with the 3.0T EA839 V6 is vastly more reliable than its B8.5 predecessor, but the ZF 8HP transmission can develop cooler and mount issues, while rare but catastrophic engine failures—likely from carbon buildup or oiling starvation—occur on high-mileage or hard-driven examples.
ZF 8HP Transmission Oil Cooler Line Leaks
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Transmission fluid pooling under car, often passenger side, Low fluid warnings on dash, Burnt fluid smell, Harsh shifting or delayed engagement when fluid gets low
Fix: Replace cooler lines and top off fluid; sometimes full cooler replacement needed if internal failure. 3-5 hours labor depending on access and whether subframe drop is required.
Estimated cost: $800-1,800
Transmission Mount Failure
Occasional · low severityTypical onset: 70,000-110,000 mi
Symptoms: Clunk on hard acceleration or deceleration, Vibration at idle in Drive, Excessive drivetrain movement felt through cabin
Fix: Replace upper transmission mount (common) or side mounts. Upper mount is 2-3 hours; if doing all mounts add another 2 hours.
Estimated cost: $400-900
In-Tank Fuel Filter Clogging
Occasional · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Rough idle or hesitation under load, Fuel trims way out of spec, Lean codes or fuel system pressure faults, Loss of power especially during hard pulls
Fix: Drop tank, replace fuel pump module or filter assembly depending on contamination. 4-6 hours labor.
Estimated cost: $900-1,500
Catastrophic Engine Failure (Piston/Bearing/Crankshaft)
Rare · high severityTypical onset: 80,000-150,000 mi
Symptoms: Sudden loss of power with heavy knock, Metal shavings in oil, Rod bearing noise that progresses rapidly, Seized engine or thrown rod through block
Fix: Often traced to carbon buildup starving oil passages, extended oil change intervals, or turbo debris. Requires engine rebuild (pistons, rings, bearings, gaskets) or short block replacement. 25-40 hours labor plus machine work if salvaging head.
Estimated cost: $8,000-15,000
Carbon Buildup on Intake Valves
Common · low severityTypical onset: 60,000-100,000 mi
Symptoms: Rough idle, especially cold start, Misfires under light load, Loss of power and throttle response, Fuel trims compensating heavily
Fix: Walnut blast cleaning both cylinder heads. 6-8 hours labor due to intake manifold and upper engine disassembly on V6.
Estimated cost: $800-1,400
Thermostat Housing Coolant Leaks
Occasional · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Coolant smell in cabin or under hood, Slow coolant loss with no visible external leak, Temperature fluctuations or overcooling, Visible leak near front of engine, driver side
Fix: Replace thermostat housing and thermostat. 3-4 hours labor, sometimes requires auxiliary coolant pump replacement at same time.
Estimated cost: $600-1,200
Buy it—this generation S4 is night-and-day better than the supercharged B8.5, just budget for carbon cleaning and keep religious oil changes to avoid the rare but wallet-destroying engine failures.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.