The 2009 S5 with the 4.2L V8 is a fantastic driver when healthy, but the engine has a catastrophic timing chain/tensioner failure mode that can destroy the motor. Transmission cooler leaks and motor mount failures are routine maintenance, but the big worry is whether the previous owner stayed on top of chain service.
Timing Chain Tensioner and Guide Failure (Engine Destruction)
Common · high severity
Typical onset: 80,000-120,000 mi
Symptoms: Cold-start rattle for 1-2 seconds that worsens over time, CEL with cam/crank correlation codes, Sudden catastrophic loss of timing leading to piston/valve contact, Metal debris in oil
Fix: Preventive replacement is engine-out, 18-24 hours labor for chains, tensioners, guides, and upper chain rails. If it fails catastrophically, you're looking at bent valves, damaged pistons, possible crankshaft damage requiring full engine rebuild or replacement. Many shops recommend doing this service proactively at 80k-100k miles.
Estimated cost: $4,500-7,000 preventive; $12,000-18,000+ if engine damage occurs
Transmission Oil Cooler Line Leaks
Common · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: Transmission fluid dripping under car, passenger side, Low trans fluid warning on dash, Burnt smell from fluid contacting exhaust, Transmission slipping or harsh shifts if fluid level drops significantly
Fix: Replace cooler lines and often the cooler itself. Lines become brittle and crack at fittings. 3-5 hours labor, includes fluid refill. Not an emergency if caught early but will strand you if fluid level drops too low.
Estimated cost: $800-1,500
Engine and Transmission Mount Failure
Common · low severity
Typical onset: 60,000-100,000 mi
Symptoms: Clunk on takeoff or when shifting into drive/reverse, Excessive engine movement visible under hard acceleration, Vibration at idle that changes when put in gear, Driveline shudder during shifts
Fix: Front and rear motor mounts and transmission mount all tend to separate or tear. Replace as a set for best results. 4-6 hours labor total. Hydro mounts lose fluid and collapse. This is wear-and-tear but dramatically affects driving feel.
Estimated cost: $1,200-2,000
Carbon Buildup on Intake Valves (Direct Injection)
Common · medium severity
Typical onset: 60,000-90,000 mi
Symptoms: Rough idle, especially when cold, Misfires under load, Loss of power and throttle response, Poor fuel economy, CEL with misfire codes
Fix: Direct injection means no fuel washing over intake valves. Walnut blasting required to remove carbon deposits. 6-8 hours labor, engine covers off, intake manifold removed. Not dangerous but significantly impacts driveability. Should be done every 60k-80k miles as preventive maintenance.
Estimated cost: $800-1,400
Water Pump and Thermostat Housing Leaks
Occasional · medium severity
Typical onset: 80,000-130,000 mi
Symptoms: Coolant leak visible at front of engine, Slow coolant loss requiring frequent top-ups, Steam or coolant smell from engine bay, Overheating if leak becomes severe
Fix: Plastic thermostat housing cracks, water pump seal fails. Often done together since access requires same work. 5-7 hours labor. The 4.2L V8 is tightly packaged so access is not great. Use OEM or equivalent parts; cheap pumps fail quickly.
Estimated cost: $1,500-2,500
PCV System and Oil Consumption Issues
Occasional · medium severity
Typical onset: 70,000-120,000 mi
Symptoms: Consuming 1 quart per 1,000-2,000 miles, Blue smoke on startup or deceleration, Rough idle, Valve cover oil leaks, Pressure buildup causing gasket failures
Fix: PCV valves integrated into valve covers fail, causing pressure issues and oil consumption. Replace both valve covers with updated versions. Also check for oil control ring issues if consumption is severe. 6-8 hours labor for valve covers; if piston rings are worn, you're into major internal work.
Estimated cost: $1,800-3,000 for valve covers; $8,000-12,000+ if internal engine work needed
Owner tips
Do the timing chain service proactively at 80k-100k miles or immediately if you hear any cold-start rattle — this is non-negotiable on the 4.2L V8
Use quality 5W-40 synthetic oil and change every 5,000 miles max; oil quality directly affects timing chain tensioner life
Budget for walnut blasting every 60k-80k miles to prevent carbon-related misfires
Inspect transmission cooler lines and motor mounts during every service — catch them before they strand you
Buy only with full timing chain service records or budget $5k-7k immediately to do it yourself; otherwise it's a hand grenade with the pin half-pulled.
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.
Fitment notes: Located in trunk on driver side; high-performance V8 requires AGM battery
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Every control module on the 2008-2016 Audi S5 — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
📍 Rear trunk lid, integrated in trunk handle or license plate area
🔧 VCDS or Autel
⚠️ Optional equipment. Calibration for parking guidelines may be needed.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2009 Audi S5 4.2L V8 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years.