The B6/B7 S4 with the 4.2L V8 (BHF/BBK) is a high-performance sedan plagued by catastrophic engine failure due to timing chain guide design flaws. When maintained meticulously and if the engine survives past 100k, it's a rewarding driver—but budget for a potential $12k-18k engine rebuild or replacement.
Timing Chain Guide Failure and Catastrophic Engine Damage
Common · high severity
Typical onset: 60,000-120,000 mi
Symptoms: rattling/clattering on cold starts that fades after warm-up, check engine light with cam/crank correlation codes, metal shavings in oil, sudden loss of power or no-start after guide fragments
Fix: Plastic timing chain guides disintegrate, sending debris through oil system and destroying bearings, pistons, cylinder walls. Requires complete engine-out rebuild (pistons, rings, bearings, guides, chains, tensioners) or used/reman engine swap. 40-60 hours labor for rebuild, 20-30 for swap.
Estimated cost: $8,000-18,000
Carbon Buildup on Intake Valves (Direct Injection)
Common · medium severity
Typical onset: 50,000-80,000 mi
Symptoms: rough idle and misfires, loss of power especially under load, increased fuel consumption, P0300-series misfire codes
Fix: Direct injection means no fuel washing valves—carbon cakes on intake valves. Requires walnut-blasting media cleaning with intake manifold removal. 6-8 hours labor, should be done every 60-80k preventively.
Estimated cost: $600-1,200
Transmission Oil Cooler Line and Thermostat Failure
Common · high severity
Typical onset: 70,000-110,000 mi
Symptoms: transmission fluid in coolant (pink milkshake in expansion tank), coolant in transmission (burnt smell, slipping, erratic shifts), transmission overheating, limp mode
Fix: Internal cooler in radiator fails, allowing cross-contamination. Requires radiator replacement, complete transmission fluid flush (multiple cycles), often torque converter replacement. If caught late, full transmission rebuild. 8-12 hours for cooler/flush, add 20+ for trans rebuild.
Symptoms: clunking over bumps, wandering or imprecise steering, uneven tire wear, vibration during braking
Fix: All 8 control arms (per axle, front and rear) have non-serviceable bushings and wear out. Audi requires full arm replacement—no press-in bushings available OEM. Aftermarket offers bushing kits but labor-intensive. Front lower arms most common. 4-6 hours for fronts, 3-4 for rears.
Estimated cost: $1,200-2,000 (front lower arms), $2,500-4,000 (all four corners)
Secondary Air Injection (SAI) System Failures
Occasional · low severity
Typical onset: 80,000-120,000 mi
Symptoms: check engine light P0410-P0412 codes, cold-start rough idle for 20-30 seconds, failed emissions testing in states that monitor readiness
Fix: SAI pump, check valves, or lines fail. System only runs first 90 seconds after cold start to heat cats. Can delete (not emissions-legal) or replace pump and valves. 2-4 hours labor depending on component.
Symptoms: single-cylinder misfires, rough running under load, flashing check engine light, reduced power
Fix: Eight individual coil packs fail over time, more common if spark plugs aren't replaced at 40k intervals. Replace all plugs and failed coils; once one coil goes, others follow. 2 hours labor.
Symptoms: coolant smell in cabin or under hood, visible coolant leak at back of engine, overheating or erratic temp gauge, low coolant warnings
Fix: Plastic coolant flanges at rear of cylinder heads crack and leak. Thermostat housing also fails. Both require upper intake manifold removal for access. Replace all coolant flanges, hoses, and thermostat together. 6-8 hours labor.
Estimated cost: $800-1,400
Owner tips
Change oil every 5,000 miles maximum with quality 5W-40 synthetic—this is non-negotiable for timing chain guide longevity.
Inspect timing chain guides via borescope at 60k and 80k; listen for cold-start rattle and pull oil filter to check for plastic debris.
Replace transmission fluid and filter every 40k miles; inspect cooler lines and radiator for cross-contamination signs early.
Walnut-blast intake valves every 60-80k miles preventively to avoid misfires and carbon-related damage.
Budget $2,000/year for deferred maintenance catch-up if buying used—these are 20-year-old German performance cars now.
Only buy if you can verify timing chain service history or are prepared to immediately fund an engine rebuild; otherwise, it's a ticking time bomb that drives beautifully until it grenades.
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 under spare tire in trunk
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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.
Performance
Horsepower
340hp
Torque
302lb-ft
0–60 mph
5.1sec
Quarter mile
13.6sec
Top speed
155mph
Capability & size
Curb weight
3,990lb
Wiper blades
B7 generation sedan (2006-2008) with 2005 overlap. Standard hook-type fitment.
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 2005 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.