The 2021 S4 (B9.5 generation) with the EA839 3.0T V6 is generally solid but has inherited some expensive engine gremlins from its MLB Evo platform siblings. The frequency-documented transmission cooler and mount failures plus alarming engine rebuild data suggest potential early oil dilution and catastrophic bearing wear in certain production batches.
Symptoms: Metallic knocking at idle that worsens with revs, Low oil pressure warning at operating temp, Fuel smell in oil during dipstick check, Excessive oil consumption (more than 1 qt per 1,000 mi)
Fix: Complete engine teardown reveals spun rod or main bearings caused by fuel washing cylinder walls during cold starts (faulty injector calibration or turbo seal leak). Requires short block replacement or full rebuild with updated pistons/rings. 25-35 labor hours plus machine work if salvaging heads.
Estimated cost: $15,000-25,000
Transmission Oil Cooler Line Leaks
Common · medium severity
Typical onset: 40,000-80,000 mi
Symptoms: Transmission fluid spots on driveway (red/brown fluid), Burning smell after highway driving, Transmission temp warning on dash, Fluid level drops requiring top-ups every few months
Fix: ZF 8HP transmission cooler hard lines corrode at crimped fittings or crack from vibration where they route near exhaust. Replacement requires partial subframe drop to access lines. 4-6 labor hours plus fluid flush.
Estimated cost: $1,200-2,000
Transmission Mount Failure
Common · low severity
Typical onset: 50,000-90,000 mi
Symptoms: Clunk when shifting from Park to Drive, Vibration at idle in Drive with brake applied, Excessive driveline lash during throttle tip-in, Visible transmission sag or torn rubber on mount inspection
Fix: Rear transmission mount (part of subframe assembly) tears from aggressive launches and torque converter lock-unlock cycles. Requires lift and subframe support to replace. 2-3 labor hours.
Estimated cost: $600-900
High-Pressure Fuel Pump Failure
Occasional · high severity
Typical onset: 60,000-100,000 mi
Symptoms: Long crank / no-start when engine is hot, Rough idle with P0087 fuel rail pressure code, Loss of power above 4,000 RPM, Metallic whining from engine bay during cranking
Fix: Bosch HPFP on these direct-injection engines fails from poor fuel quality or camshaft lobe wear. Requires intake manifold removal to access pump on back of cylinder head. Often replace cam follower simultaneously. 5-7 labor hours.
Estimated cost: $2,000-3,200
Rear Axle Carrier Bushing Knock (Recall 21V-870)
Occasional · medium severity
Symptoms: Clunking from rear during direction changes or over bumps, Steering wheel off-center after alignment, Uneven rear tire wear on inside edges, Rear end feels loose or vague in corners
Fix: Rear subframe carrier bushings (part of Quattro diff mounting) were improperly installed at factory causing premature wear. Audi recall replaces bushings and realigns. If out of recall window: 3-4 labor hours plus alignment.
Estimated cost: $0 (recall) or $800-1,400
Turbocharger Wastegate Rattle
Occasional · low severity
Typical onset: 70,000-110,000 mi
Symptoms: Metallic rattling from engine bay at idle (sounds like diesel), Rattle disappears above 1,500 RPM, No performance loss or codes initially, Eventually triggers P0234 overboost or underboost codes
Fix: Single twin-scroll turbo's internal wastegate actuator rod wears loose in bracket. Requires turbo removal and rebuild or replacement. If caught early, some shops can shim the actuator. 8-10 labor hours for turbo R&R.
Estimated cost: $2,800-4,500
Owner tips
Change oil every 5,000 mi with 0W-40 Euro spec (not factory 10k interval) to combat fuel dilution issues — send used oil sample to Blackstone at 30k and 60k miles to catch bearing wear early
Inspect transmission cooler lines annually and wrap any areas near exhaust with heat shielding
Use Top Tier fuel exclusively and add fuel system cleaner every other tank to keep HPFP and injectors healthy
If buying used, demand oil analysis history and borescope inspection of cylinder walls — walk away if seller refuses
Buy only with comprehensive records and pre-purchase inspection including oil analysis; the engine bearing lottery makes this a $20k gamble without documentation, but well-maintained examples are phenomenal daily drivers.
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.
Be the first to unlock repairs for the 2021 Audi S4
Procedures haven't been generated for this vehicle yet. Become the founding sponsor and we'll generate expert-grade, step-by-step repair walkthroughs for every common job on it — free for every mechanic and DIYer who looks it up after, forever.
Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2021 Audi A8, RS7, RS6 Avant, RS5 Sportback, RS5 Coupe, Q8, Q7, Q5 Sportback, S4 Sedan, Q5, A7, A6, A6 Allroad, A5 Sportback, A5 Coupe, A5 Cabrioleet, A4 Sedan, A4 Allroad, E-Tron Sportback Quattro, SQ7, S5 Cabriolet, E-Tron Quattro, SQ8, SQ5 Sportback, SQ5, S8, S7, S6 Sedan, S5 Sportback, S5 Coupe, 2022 E-Tron GT, and 2021-2022 RSQ8 vehicles. Due to a software issue, a blank or black screen may be displayed instead of the rearview camera image when the vehicle is placed in reverse gear. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 111, "Rear Visibility."
Consequence: A blank rearview camera display can reduce the driver's rear visibility, increasing the risk of a crash.
Remedy: Dealers will update the infotainment unit software, free of charge. Owner notification letters were mailed October 25, 2022. Owners may contact Audi's customer service at 1-800-253-2834. Volkswagen's number for this recall is 91DZ.
TIRES · 22V034000
2022-01-26
Volkswagen Group of America, Inc. (Audi) is recalling certain 2019-2021 Audi A5 Sportback, RS5 Coupe, RS5 Sportback, S5 Sportback, 2020-2021 A4 Allroad, A4 Sedan, A5 Cabriolet, A5 Coupe, A6 Allroad, A6 Sedan, A7, A8, Q5, S4 Sedan, S5 Coupe, S5 Cabriolet, S6 Sedan, S7, S8, SQ5, 2021 Q5 Sportback, Q7, Q8, RS6 Avant, RS7, RSQ8, SQ5 Sportback, SQ7, and SQ8 vehicles. The rear axle alignment may not have been inspected after the repairs for Recall 21V-295 (42L1) were performed.
Consequence: Rear axle misalignment may cause premature or uneven tire wear, increasing the risk of a crash.
Remedy: Dealers will inspect the rear axle, adjust the alignment as necessary, and replace any prematurely or unevenly worn tires, free of charge. Owner notification letters were mailed March 3, 2022. Owners may contact Audi customer service at 1-800-253-2834. Audi's number for this recall is 42L5.
SEAT BELTS:REAR/OTHER:RETRACTOR · 21V606000
2021-08-05
Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2021 Volkswagen ID4, Audi A4 Allroad, A4 Sedan, A5 Cabriolet, A5 Coupe, A5 Sportback, A6 Allroad, A6 Sedan, A7, A8, E-Tron Quattro, E-Tron Sportback Quattro, Q3, Q5, Q5 Sportback, Q7, Q8, RS5 Sportback, RS5 Coupe, RS6 Avant, RS7, RSQ8, S4 Sedan, S5 Cabriolet, S5 Coupe, S5 Sportback, S6 Sedan, S7, S8, SQ5, SQ5 Sportback, SQ7, SQ8, and 2021-2022 S3 Sedan vehicles. The rear seat belt automatic locking retractors may deactivate early, which can prevent the child restraint system from securing properly. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 208, "Occupant Crash Protection."
Consequence: An unsecured child restraint system can increase the risk of injury during a crash.
Remedy: Dealers will inspect, and replace as necessary, the middle-rear seat belt assemblies, free of charge. Owner notification letters were mailed August 27, 2021. Owners may contact Volkswagen customer service at 1-800-893-5298 and Audi customer service at 1-800-253-2834. Volkswagen's numbers for this recall are 69CR (VW) and 69CS (Audi).
Volkswagen Group of America, Inc. (Audi) is recalling certain 2021 Q7, Q8, Q5 Sportback, SQ5 Sportback, RS6 Avant, RS7, RS Q8, 2020-2021 Audi S6 sedan, Q5, A8, S8, A7, A6 Allroad, A5 Cabriolet, A4 sedan, A4 Allroad, SQ5, S7, A6 sedan, S5 coupe, S4 sedan, S5 Cabriolet, A5 coupe, 2019-2021 RS5 coupe, A5 Sportback, S5 Sportback, RS5 Sportback vehicles. The lock nut on the trailing arm of the rear axle may break due to stress corrosion.
Consequence: A broken lock nut may misalign the rear axle, causing a loss of control and increasing the risk of a crash.
Remedy: Dealers will replace the lock nuts and, if necessary, the associated bolts, free of charge. Owner notification letters were mailed June 4, 2021. Owners may contact Audi customer service at 1-800-253-2834. Audi's number for this recall is 42L1.
Building an app?
Free API access to all this data — 50 requests/day, no card required.