What goes wrong, what it costs, and what to check before you buy a used Audi S4.
The Audi S4 occupies a niche position on the UK market.
We track 5 known issues across the Audi S4 range, with 2 classified as significant. Knowing which variants and configurations to approach with caution can save you from expensive surprises after purchase.
Found a Audi S4? Enter the reg to see which of our 5 known issues apply to that exact car, plus full MOT history and mileage checks.
B6 (1999–2005) — Engine options included the 2.7 Twin Turbo V6, 4.2 V8. 1 known issues affect this generation, none rated as critical. The most significant concern is Suspension joint wear (£300–£600 to address).
B7 (2005–2008) — Engine options included the 4.2 V8. 1 known issues affect this generation, none rated as critical. The most significant concern is Suspension joint wear (£300–£600 to address).
B8 (2009–2016) — Engine options included the 3.0 Supercharged V6. We track 4 known issues on this generation, with 2 classified as significant. The most significant concern is Water pump failure (£400–£600 to address).
The water pump on the 3.0 supercharged V6 engine uses a plastic impeller that becomes brittle with age and thermal cycling. The impeller can break apart or the pump bearing can fail, causing complete coolant circulation loss. This engine runs extremely hot under load and will suffer catastrophic damage within minutes if the cooling system fails. The plastic thermostat housing commonly fails at the same mileage, making joint replacement economical.
Complete pump failure causes total coolant circulation loss and engine overheating within 2-3 minutes of driving. The supercharged V6 will suffer irreversible head gasket failure, cylinder head warping, or complete engine seizure. Total repair costs can exceed £8,000. The car should not be driven if pump failure is suspected.
Check the coolant level and look for any white residue or staining around hoses, the expansion tank and radiator. After a test drive, check the temperature gauge stayed stable and look underneath for drips. Ask whether key cooling components have been replaced.
The mechatronic unit controls the DSG dual-clutch transmission and contains hydraulic valves, solenoids, and electronic control circuits. Internal wear of the valve body and contamination from degraded transmission fluid causes erratic gear changes, failure to engage gears, and complete transmission shutdown. The unit requires precise pressure control for clutch engagement and any malfunction affects drivability. Regular fluid changes significantly extend unit life but many owners skip this service.
Mechatronic failure can cause complete loss of drive without warning, potentially leaving the vehicle stranded. Repair requires transmission removal and mechatronic unit replacement or reconditioning, typically costing £2,500-4,000. Some failures damage the clutch packs, increasing repair costs further. The vehicle should not be driven once transmission warnings appear.
Test the automatic gearbox extensively in slow traffic, car parks and on hill starts. Feel for any juddering, hesitation or clunking during gear changes. Try repeated low-speed manoeuvres as this is where problems are most apparent.
The thermostat housing on the 3.0 supercharged engine is made from plastic and develops stress cracks from repeated thermal cycling. The housing typically cracks around the mounting bolts or where the coolant hoses connect, causing external coolant leaks. While not immediately dangerous like water pump failure, the leak will worsen over time and can lead to overheating if left unrepaired. Often replaced together with the water pump as a preventive measure.
A cracked housing will leak coolant at an increasing rate as the crack expands. Complete housing failure can cause significant coolant loss and overheating. Repair involves draining the cooling system and typically costs £300-700 depending on whether other cooling components are replaced at the same time.
Check the coolant level and look for any white residue or staining around hoses, the expansion tank and radiator. After a test drive, check the temperature gauge stayed stable and look underneath for drips. Ask whether key cooling components have been replaced.
The positive crankcase ventilation (PCV) valve on the 3.0 supercharged engine regulates crankcase pressure by allowing combustion gases to be burned in the intake. The valve contains a diaphragm that hardens and splits over time, causing vacuum leaks and unmetered air entering the engine. This results in rough idle, increased oil consumption, and potential damage to the mass airflow sensor from oil vapour contamination.
A failed PCV valve allows unmetered air into the engine, causing lean running conditions and rough idle. Oil vapour can contaminate the mass airflow sensor, causing poor engine performance and potentially requiring sensor replacement. Oil consumption will increase as crankcase pressure forces oil past seals and gaskets.
Check the oil level before the engine is started. Ask the seller how often they top up the oil between services. After a test drive, check the level again and look behind the car for blue or grey exhaust smoke under acceleration.
The B6 and B7 S4 models show significantly higher rates of suspension joint and bush wear compared to the fleet average, particularly affecting the front control arm bushes and anti-roll bar links. The 4.2 V8 variants are especially prone to this issue, with MOT data showing 9.4 times the fleet average failure rate. The additional weight and performance-oriented suspension setup accelerates wear of rubber components, leading to clunking noises and imprecise handling.
Worn suspension joints affect handling precision and can cause uneven tyre wear. While not immediately dangerous, severely worn joints can separate completely, causing loss of control. Typical repair involves replacing multiple bushes and joints, costing £400-800 depending on which components are affected.
Listen for knocking, clunking or rattling over bumps during the test drive. Inspect the underside for corroded or cracked suspension components. Check the MOT history for suspension-related advisories, which often predict future failures.
For the full breakdown of all 5 tracked issues with repair costs, see the Audi S4 common problems page.
Based on 6k real DVSA MOT tests, the Audi S4 fails more often than average on several items. The biggest outlier is seat mounting fault at 51x the fleet average, followed by brake hoses perished or damaged (35x).
When viewing a specific car, check its MOT history for recurring advisories in these categories. See the full Audi S4 MOT failure breakdown for data at every mileage point.
Routine servicing (oil and filter change every 10k miles) typically costs £80–£120 at an independent garage.
The bigger-ticket items to budget for include dsg transmission fluid (£300–£450).
See the full Audi S4 service schedule for every interval and cost breakdown.
The Audi S4 is a reasonable used buy provided you check for the issues outlined above. None of the problems we track are insurmountable, but they do reward buyers who inspect thoroughly and verify the service history before committing.
Before committing, check the car's full MOT history, verify the service record is complete, and if possible arrange a specialist inspection. Enter any registration into our free report to see the complete picture.
Get Car Wise maintains a database of known mechanical issues for every popular car on UK roads, tracking the faults that owners, specialists and DVSA data reveal.
When you run a report on a specific Audi S4, we cross-reference the exact variant, engine and age against our database of 5 known issues. Combined with full MOT history analysis, mileage verification and DVLA data, you get a complete picture before viewing.
Enter the registration for MOT history, mileage verification, known faults for that exact variant, and a Get Car Wise Score.
This guide was compiled from independent expert reviews, DVSA MOT data, specialist workshops and our own database of 5 known Audi S4 issues. We are not affiliated with any source listed.