The B9 S4 replaced the previous generation's supercharged V6 with a single-turbocharged 3.0-litre V6 from the EA839 family, producing 354 hp and 500 Nm through a ZF 8-speed torque converter automatic and permanent quattro. In Europe, the petrol 3.0 TFSI was sold only from 2016 to 2018 before WLTP reforms led to its replacement by a 3.0 TDI diesel for the B9.5 facelift. The turbocharged V6 is shared with the RS4/RS5 (in 2.9T bi-turbo form) and Porsche Macan/Cayenne, giving it a broad parts and knowledge base.· more· less
Water pump design flaw on EA839Rocker arm failures on early cars
Buy if: You want a refined performance sedan with proven drivetrain components and can verify the water pump revision and rocker arm update status.
Avoid if: You cannot budget for potential cooling system or engine internals repairs, or are looking at an early 2017 car with unconfirmed rocker arm revision.
Factory water pump leaks internally, allowing coolant to migrate into the vacuum system · more· less
The EA839 3.0T uses a mechanical water pump with a vacuum-operated slide valve controlling impeller actuation. This design has an inherent flaw: when the pump fails, it leaks coolant internally into the engine's vacuum system rather than externally. The coolant can then contaminate the vacuum solenoid valve, coolant bypass valve, and other components. Symptoms include gradual coolant loss, dashboard warnings, and P0299 codes. The revised pump uses a 6-bolt pulley (original has 4 bolts). Dealer repair including water pump, vacuum solenoid, coolant bypass valve, gaskets, and labor typically runs €3,000-4,000. Independent specialists may complete the work for €1,500-2,500. This issue affects all model years but tends to appear after 60,000-100,000 km.
Rocker arm bearing failure
up to €4,0002 of 7
Roller bearings in the rocker arms wear prematurely, causing valvetrain ticking and potential camshaft damage · more· less
Early EA839 engines (primarily 2017-2018 production) suffered from premature rocker arm bearing failure. The needle bearings inside the roller rockers would wear through, creating a distinctive loud ticking noise. If ignored, the worn rocker arms can damage the camshaft lobes. Audi revised the rocker arm design in August 2018, making the bearings larger and the shaft smaller for improved durability. The updated part number starts with 0P2 (replacing 06M). Cars built before mid-2018 with original rocker arms remain vulnerable. Replacement of all 24 rocker arms plus potentially damaged camshafts runs €1,500-4,000 depending on the extent of damage. No formal recall was issued, and Audi handled many early repairs as goodwill, which is a voluntary contribution rather than a warranty entitlement, so what a given car gets depends on its history and its dealer.
Piston skirt wear and failure
up to €12,0003 of 7
Design flaw causes excessive piston rocking, leading to skirt wear and potential engine damage · more· less
The EA839 has a documented piston instability issue where the pistons rock laterally in the cylinders, causing uneven skirt wear. Additionally, machined oil control ring drain holes act as stress risers that can initiate cracks in the ringlands. Symptoms include a diesel-like clacking noise (piston slap), increased oil consumption, rough idle, and eventually blue exhaust smoke. Audi has released three different piston revisions during EA839 production, acknowledging the issue. While the overall failure rate is estimated below 5%, one dealership reported 14 stock-car failures in a 6-week period. The eight-year, roughly 130,000 km piston skirt extension often quoted here is AWA-25-08, an Audi of America programme for the United States and Puerto Rico. No equivalent European entitlement is established, so a European buyer should treat any help as goodwill rather than assume cover. Repair involves engine rebuild or piston replacement at €4,000-12,000 depending on damage extent.
PCV system check valve failure
up to €8004 of 7
PCV check valve fails, allowing crankcase pressure to push oil past the oil filler cap · more· less
The Positive Crankcase Ventilation system on the EA839 has a check valve integrated into the PCV hose on the driver's side cylinder head. When this valve fails, positive air pressure flows back into the crankcase instead of being properly vented. This causes oil seepage around the oil fill cap, and in severe cases the cap can blow off entirely while the engine is running, spraying oil across the engine bay. Audi released a Technical Service Bulletin with an improved hose and check valve assembly. The part cost is modest (€100-200), and labor runs 1-2 hours at a specialist. The main risk is catching it early before oil sprays onto hot components.
Oil filter housing leak
up to €2,5005 of 7
Plastic oil filter housing warps from heat cycles, causing oil leaks into the engine valley · more· less
The oil filter housing sits at the front of the engine, directly before the turbocharger wastegate actuator. The plastic housing warps from repeated heat cycles, and the gasket flattens over time. Oil leaks into the engine valley and can be mistaken for an oil pan leak due to its position. Replacement is labor-intensive as the turbocharger must typically be removed for access. An aftermarket aluminum housing upgrade (around €200-300 for the part) eliminates the issue permanently. With labor, expect €800-1,500 at a specialist, or up to €2,500 at a dealer.
Active engine mount failure
up to €1,5006 of 7
Hydraulic-filled active motor mounts leak or the electronic control solenoid fails · more· less
The S4 B9 uses active engine mounts with an ECU-controlled electric valve that adjusts stiffness. At idle, the valve opens to allow oil to move freely between chambers for smoother operation. These mounts typically fail between 80,000-130,000 km through either hydraulic fluid leaks or electrical solenoid failure. Symptoms include increased vibration at idle and a noticeable clunk when shifting into gear. OEM replacement runs €250-400 per mount plus labor. Aftermarket solid mounts from 034Motorsport or similar are available for less but sacrifice some NVH refinement.
Cylinder 6 misfire
up to €8,0007 of 7
Intermittent misfire on cylinder 6 under specific load conditions, cause not fully understood · more· less
On both stock and tuned EA839 engines, cylinder 6 misfires have been reported under specific load conditions. The exact root cause remains unclear, though theories include uneven cooling across the V6 bank and injector variance. In mild cases, replacing the ignition coil and spark plug for the affected cylinder resolves the issue (€100-500). In severe cases where the misfire has caused physical damage to the piston or cylinder wall, significant engine work may be required. This is a less common issue overall but worth monitoring through diagnostic scans.
Capable engine with known design flaws that need proactive monitoring
The EA839 3.0T is a strong and responsive engine, but it has several documented design weaknesses, particularly in the cooling system and early-production valvetrain. The water pump flaw is the most concerning as it affects all model years and can cause cascading damage if coolant migrates through the vacuum system. The piston skirt issue is rare, and the eight-year extension that prompted so much discussion is a North American programme rather than a European one. Cars built after mid-2018 with revised rocker arms and updated PCV components are notably more reliable. With proper inspection and proactive maintenance, many S4 B9s reach 150,000+ km without major issues.
Service history
Complete Audi dealer or specialist records essential. Verify oil changes every 15,000 km or 12 months.
Tires
Check tread depth, age (date codes), and uneven wear patterns. 19-inch tires wear faster on the S4.
Cold start
Start engine completely cold. Listen for any abnormal ticking, rattling, or diesel-like clacking in the first 30 seconds.
Test drive
Minimum 30 minutes including motorway speeds. Let engine and transmission reach full operating temperature.
Specific for this vehicle
Check water pump pulley bolt pattern
Revised water pump has a 6-bolt pulley (original has 4 bolts). If still on the 4-bolt version, budget for replacement.
Listen for valvetrain ticking on cold start
A persistent loud tick after startup indicates rocker arm wear. Check if the car was built before August 2018 and whether updated rocker arms (0P2 part number) have been fitted.
Inspect coolant level and condition
Low coolant without visible external leaks suggests internal water pump failure. Check for coolant residue on the front engine block.
+ 4 more checksShow less
Check oil filler cap seating
Oil residue around the filler cap suggests PCV valve failure. The cap should seat firmly without any oil seepage.
Run full diagnostic scan
Check for stored fault codes relating to misfires (especially cylinder 6), coolant system warnings, PCV pressure, and transmission adaptation values.
Inspect engine mounts for leaks
Look for hydraulic fluid weeping from the active engine mounts. Excessive vibration at idle is also a sign of failure.
Verify piston skirt warranty status
The eight-year, 130,000 km piston skirt programme is North American. Ask Audi whether any piston work has been performed on this car and what goodwill, if any, would apply here.
Recalls and Technical Service Bulletins
Defective seat back weld that could increase injury risk - European campaign 72G1, VIN-specific B9 A4-family vehicles including S4 built August to September 2016Critical - verify completed
Contact Audi with the VIN: the seat back campaign is VIN-specific and covers a two-month build window at the start of B9 production. Several items often listed against the S4 are North American and do not describe this European car: the passenger seat heater and occupant detection recall 21V874, covers model-year 2018 to 2020 sedans in that market, the infotainment items 22V742 and 22V806 concern later facelift cars, the rear seat belt retractor recall 21V606, covers model-year 2021 cars, and AWA-25-08 is a warranty extension for the United States and Puerto Rico rather than a recall.
Warranty Status
Factory warranty (2 years)Expired on all used B9 S4 petrol models
Piston skirt programme (North America only)AWA-25-08 covers the United States and Puerto Rico; European cars have no equivalent published entitlement
Rust perforation warranty12 years from first registration
All petrol B9 S4 models (2016-2018 in Europe) are outside their original 2-year factory warranty. The much-quoted piston skirt extension is an Audi of America programme, so a European car cannot rely on it; ask Audi what goodwill applies using the VIN.
Sources: Research draws on model-specific owner forums and owner communities, recall information from official authorities, German automotive press, and multiple workshop cost references cross-checked against each other.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.
