The B7 S4 with the 4.2L V8 is a stellar performer when maintained, but the timing chain guide and carbon buildup issues can turn expensive fast. Budget for preventive maintenance or walk away.
Timing Chain Guide and Tensioner Failure
Common · high severity
Typical onset: 80,000-120,000 mi
Symptoms: rattling on cold start that fades after warmup, metallic noise from front of engine, check engine light with cam/crank correlation codes, catastrophic engine failure if guides break
Fix: Engine-out job requiring front-end removal, all guides, tensioners, and chains replaced. 20-25 labor hours at a competent indie shop. Do NOT delay once rattling starts.
Estimated cost: $4,500-7,000
Carbon Buildup on Intake Valves
Common · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: rough idle and misfires, loss of power especially under load, poor fuel economy, multiple misfire codes
Fix: Direct injection means no fuel washing valves. Walnut blasting required every 60-80k miles. 4-6 labor hours, intake manifold removal.
Estimated cost: $600-1,200
Front Control Arm Bushings
Common · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: clunking over bumps, steering wander and vague turn-in, uneven tire wear, vibration through steering wheel
Fix: OEM arms are not rebuildable; requires full control arm replacement on both sides. 3-4 hours labor, alignment required after.
Estimated cost: $800-1,400
Oil Consumption from Piston Ring Land Failure
Occasional · high severity
Typical onset: 90,000-150,000 mi
Symptoms: burning 1+ quart every 1,000 miles, blue smoke on startup or deceleration, fouled spark plugs, eventually leads to complete engine failure
Fix: Known FSI engine defect. Requires full engine rebuild or short block replacement. 30-40 labor hours. Some had extended warranty coverage; check service history.
Estimated cost: $8,000-15,000
Transmission Cooler and Mount Failures
Occasional · medium severity
Typical onset: 80,000-130,000 mi
Symptoms: transmission fluid leaking from cooler lines, harsh shifts or slipping, clunking when shifting from park to drive, vibration at idle in gear
Fix: Cooler lines crack at fittings; mounts collapse from V8 torque. Cooler is 2-3 hours, mounts are 1-2 hours each. Do mounts when doing clutch or major service.
Estimated cost: $400-1,000
Supercharger Bypass Valve and Diverter Valve Leaks
Occasional · low severity
Typical onset: 70,000-120,000 mi
Symptoms: hissing sound under hood during acceleration, slight loss of boost pressure and power, rough idle occasionally, check engine light for boost pressure codes
Fix: Diaphragms tear in valves over time. Replacements are straightforward, 1-2 hours labor. Use OEM or quality aftermarket; cheap parts fail quickly.
Estimated cost: $300-600
Window Regulator Failure
Common · low severity
Symptoms: slow or jerky window operation, window drops into door and won't raise, grinding or clicking noise from door
Fix: Plastic gears strip in regulators. 1.5-2 hours per door, door panel removal required. Common on all four windows eventually.
Estimated cost: $350-550
Owner tips
Listen for cold-start rattles on test drive; timing chain noise is a dealbreaker unless severely discounted
Budget $1,500/year for carbon cleaning and preventive maintenance if buying high-mileage
Check service records for oil consumption complaints or engine work; ring land failures often start subtly
Use only 5W-40 full synthetic and keep oil topped off; low oil accelerates timing chain wear
Test all windows, check for control arm play during inspection; these nickel-and-dime items add up fast
Buy only with documented timing chain service and clean compression test; otherwise you're gambling with a $6k repair bill at any moment.
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: AGM battery required; located in trunk under floor panel
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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.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 18V427000
2018-06-22 · EA15001
Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2005-2008 Audi A4 Sedan, A4 Avant, S4 Avant and S4 Sedan, 2007-2008 RS4 Sedan, 2004 RS4 Cabriolet, 2007-2009 A4 Cabriolet and S4 Cabriolet, 2005-2011 A6 Sedan, 2006-2011 A6 Avant, and 2007-2011 S6 Sedan vehicles. These vehicles are equipped with certain air bag inflators assembled as part of the passenger frontal air bag modules used as original equipment or replacement equipment. In the event of a crash necessitating deployment of the passenger frontal air bag, these inflators may explode due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.
Consequence: An inflator explosion may result in sharp metal fragments striking the driver or other occupants resulting in serious injury or death.
Remedy: Audi has notified owners, and dealers will replace the passenger frontal air bag with an alternate remedy part, free of charge. The recall began June 29, 2018. Owners may contact Audi customer service at 1-800-253-2834. Volkswagen's number for this recall is 69R7. Note: This recall supersedes recalls 16V382, 17V032 and 18V004 and includes vehicles that may have had their air bag previously replaced under one of those campaigns.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 17V032000
2017-01-11 · EA15001
Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2009 Audi A4 Cabriolet, S4 Cabriolet, A6 Avant, A6 Sedan and S6 Sedan vehicles originally sold, or ever registered, in Arizona, Arkansas, Delaware, the District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, and West Virginia, or "Zone B."
Additionally, unless included in "Zone B" above, Volkswagen is recalling certain 2005-2008 Audi A4 Avant, A4 Sedan, A6 Sedan, S4 Avant and S4 Sedan vehicles, 2007-2008 A4 Cabriolet, RS4 Sedan, S4 Cabriolet and S6 Sedan vehicles, and 2006-2008 A6 Avant and 2008 RS4 Cabriolet vehicles originally sold, or ever registered, in Alaska, Colorado, Connecticut, Idaho, Iowa, Maine, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New York, North Dakota, Oregon, Rhode Island, South Dakota, Utah, Vermont, Washington, Wisconsin, and Wyoming.
These vehicles are equipped with certain air bag inflators assembled as part of the passenger frontal air bag modules used as original equipment or replacement equipment. In the event of a crash necessitating deployment of the front air bags, these inflators may rupture due to propellant degradation occurring after long-term exposure to absolute humidity and temperature cycling.
Consequence: An inflator rupture may result in metal fragments striking the vehicle occupants resulting in serious injury or death.
Remedy: Audi will notify owners, and dealers will replace the passenger frontal air bag inflator, free of charge. The recall began March 30, 2018. Owners may contact Audi customer service at 1-800-253-2834. Note: This recall has been superseded by recall number 18V427.
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 2006 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 Mechanic · 20+ years.