The B6 S4 with its 4.2L V8 is a driver's car with solid handling and great exhaust note, but it's plagued by catastrophic timing chain guide failures and secondary air injection issues that can financially total an otherwise solid chassis.
Timing Chain Guide and Tensioner Failure
Common · high severity
Typical onset: 60,000-120,000 mi
Symptoms: cold-start rattle for first 2-3 seconds, metal shavings in oil, CEL with cam correlation codes, catastrophic engine failure if guides break
Fix: Engine-out job requiring complete disassembly to replace guides, tensioners, chains, and cam adjusters. 25-35 labor hours. Often combined with other preventive work while engine is out.
Estimated cost: $4,500-7,500
Secondary Air Injection System Failure
Common · medium severity
Typical onset: 70,000-150,000 mi
Symptoms: P0411 or P0491 codes, check engine light on startup, failed emissions test, pump whine or silence when it should run
Fix: SAI pump motor and/or valves fail. Pump replacement is 3-4 hours, combo valves add another 2-3 hours. Many delete the system entirely where legal.
Estimated cost: $800-1,800
Control Arm Bushings and Ball Joints
Common · medium severity
Typical onset: 80,000-120,000 mi
Symptoms: clunking over bumps, wandering on highway, uneven tire wear, steering feels vague
Fix: Front control arms wear bushings and ball joints. Best practice is replacing entire arms rather than pressing bushings. 6-8 hours for full front suspension refresh.
Estimated cost: $1,200-2,000
Transmission Mounts and Coolant Leaks
Common · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: clunk on 1-2 shift, hard downshift under braking, coolant smell in cabin, drips under center of car
Fix: Rear transmission mount fails causing drivetrain movement. Transmission oil cooler lines corrode and leak at banjo fittings. Mount is 2-3 hours, cooler lines add 3-4 hours if trans must drop.
Estimated cost: $600-1,400
Carbon Buildup on Intake Valves
Occasional · low severity
Typical onset: 80,000-150,000 mi
Symptoms: rough idle, hesitation on acceleration, reduced fuel economy, misfires under load
Fix: Direct injection design allows carbon deposits on valve backs. Walnut blasting required every 80-100k miles. 4-6 hours labor.
Estimated cost: $600-1,000
Radiator and Coolant Flange Leaks
Occasional · medium severity
Typical onset: 100,000-150,000 mi
Symptoms: coolant puddles under car, sweet smell, low coolant warning, overheating if ignored
Fix: Plastic radiator end tanks crack, coolant flanges on cylinder heads become brittle. Radiator is 3-4 hours, flanges require intake manifold removal adding 8-10 hours total.
Estimated cost: $800-2,200
Brake Pressure Accumulator (ABS Pump)
Rare · high severity
Typical onset: 120,000-180,000 mi
Symptoms: ABS and brake warning lights, hard brake pedal, pump runs constantly, extended stopping distance
Fix: Accumulator sphere loses nitrogen charge or pump fails. 2-3 hours labor, but part is expensive. Brake system must be bled properly after replacement.
Estimated cost: $1,500-2,500
Owner tips
Change oil every 5,000 miles with quality 5W-40 synthetic — timing chain life depends on it
Inspect timing chain guides via borescope at 60k if no service history exists
Budget $1,000/year maintenance minimum after 80k miles — this is not a Honda
Find a specialist Audi shop that knows these engines — dealerships often misdiagnose
Buy only if timing chains were already done and you have a $3k-5k emergency fund — otherwise you're gambling with a grenade.
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: Battery located under spare tire in trunk; requires DIN/Euro sizing; H8 group may also fit
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Every control module on the 2004-2007 Audi S4 — 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.
📍 Integrated into ABS module or separate module in trunk
🔧 VCDS
⚠️ Optional; indirect TPMS using ABS wheel speed sensors; relearn procedure after tire rotation
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.
ON CERTAIN PASSENGER VEHICLES, THERE IS A POSSIBILITY OF XENON HEADLAMP COATING DEGRADATION OVER TIME. THE LUMINOUS TRANSMITTANCE OF THE HEADLAMP MAY DECREASE OVER A PERIOD OF TIME.
Consequence: THIS CONDITION COULD AFFECT A DRIVER'S FIELD OF VIEW, INCREASING THE RISK OF A CRASH.
Remedy: DEALERS WILL REPLACE THE LEFT AND RIGHT XENON HEADLAMP REFLECTORS FREE OF CHARGE. THE RECALL BEGAN ON APRIL 11, 2005. OWNERS MAY CONTACT AUDI AT 1-800-822-2834.
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 2004 Audi S4 4.2L V8 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.