Audi S4 MOT Failures
An analysis of 6,369 real DVSA MOT tests on the Audi S4 — what fails, how often, and how that compares to every other car on UK roads. Generations covered: B6 (1999–2005), B7 (2005–2008), B8 (2009–2016).
Where the Audi S4 fails its MOT
The single biggest MOT failure point on the Audi S4 is brake hoses perished or damaged — this model is 35 times more likely to fail on this item than the average car on UK roads. That makes it a significant weak point for anyone buying or owning this model. Across 6,369 MOT tests, 19.07% of all Audi S4 tests recorded this as a failure.
Brake failures on the MOT range from worn pads and discs (routine maintenance) to corroded brake lines and seized calipers (more serious). Check for any pulling under braking and listen for grinding.
Other notable weak points include suspension joint dust cover missing or no longe... (18x the fleet average), suspension joint dust cover severely deteriorated (10x the fleet average), anti-roll bar links worn (9.4x the fleet average), and tyre seriously damaged (6.8x the fleet average). These ratios compare the Audi S4's failure rate on each item against the national average for all cars tested — a ratio of 10x means this model fails ten times more often than a typical car.
The failures span 6 categories: Brakes, Suspension, Tyres, Seatbelts & Airbags, Lights & Electrics and others. If you're inspecting a Audi S4 before purchase, these are the areas to focus on — and if any have been flagged as advisories on a previous MOT, they're likely to become failures in the near future.
How failures change with mileage
The Audi S4's weak points shift as the car covers more miles. Understanding these patterns helps you know what to expect — and what to budget for — at each stage of ownership.
Under 60,000 miles
At this mileage, most failures are either design-related or caused by age rather than wear. Components like bushes and drop links may not have been replaced yet, and original-fit parts can deteriorate even on low-mileage cars that spend a lot of time sitting.
The standout failure at this mileage is suspension pin, bush or joint worn at 5.0x the fleet average.
60,000 to 100,000 miles
This is where routine wear items start to show up. Brake components, tyres, and exhaust parts have done serious work by this point. Cars that have been well serviced will show fewer of these failures — this mileage band is where good maintenance really separates the well-kept from the neglected.
For the Audi S4 specifically, the DVSA data shows the most common failures at this mileage are brake hoses perished or damaged (35x the average) and suspension joint dust cover missing or no longe... (18x). suspension joint dust cover severely deteriorated (10x) and anti-roll bar links worn (9.4x) also appear frequently.
Over 100,000 miles
High-mileage cars accumulate failures across multiple systems. The key question isn't whether things will need doing — they will — but whether the car has been maintained well enough to keep on top of them. Look for a consistent service history and recent MOT passes with minimal advisories.
For the Audi S4 specifically, the DVSA data shows the most common failures at this mileage are seat mounting fault (51x the average) and light unit fault (16x). brake hoses perished or damaged (9.7x) and suspension joint dust cover missing or no longe... (9.2x) also appear frequently.
The shift from suspension pin, bush or joint worn at lower mileages to seat mounting fault at higher mileages is typical — early failures tend to be design or factory-related, while high-mileage failures reflect accumulated mechanical wear. A car that's been well maintained will usually dodge the worst of both.
Known issues beyond the MOT
An MOT only tests roadworthiness at a single point in time — it won't catch developing faults, intermittent problems, or issues that haven't yet reached the failure threshold. These are the issues that Audi S4 specialists and owners flag most frequently, drawn from manufacturer technical bulletins, workshop data, and verified owner reports.
Water pump failure (B8) Major
The water pump on the 3.0 supercharged V6 engine uses a plastic impeller that becomes brittle with age and thermal cycling. Affects B8; typical independent garage repair cost is £400–£600.
DSG mechatronic unit failure (B8) Major
The mechatronic unit controls the DSG dual-clutch transmission and contains hydraulic valves, solenoids, and electronic control circuits. Affects B8; typical independent garage repair cost is £2,500–£3,500.
Thermostat housing failure (B8)
The thermostat housing on the 3.0 supercharged engine is made from plastic and develops stress cracks from repeated thermal cycling. Affects B8; typical independent garage repair cost is £250–£400.
PCV valve failure (B8)
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. Affects B8; typical independent garage repair cost is £150–£250.
For the complete picture — including repair costs across independent, specialist, and dealer garages — see the full Audi S4 common problems breakdown.
What to check before buying a Audi S4
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Audi S4:
Brakes — check for brake hoses perished or damaged. Suspension — check for suspension joint dust cover missing or no longe..., suspension joint dust cover severely deteriorated, anti-roll bar links worn.
Beyond the MOT items, ask specifically about water pump failure and dsg mechatronic unit failure. These won't show up on a standard MOT but can be expensive to fix — repairs start from £400. A specialist pre-purchase inspection is worth the investment on this model.
Always check the car's full MOT history for patterns — recurring advisories often become failures within 12 months. And verify the service history to confirm maintenance has been kept up to schedule. Enter any reg into our free car check to see the complete picture.
Looking at a specific Audi S4?
Enter the reg to see its full MOT history, mileage records, write-off status, and finance checks.
Audi S4 MOT FAQs
What are the most common MOT failures on a Audi S4?
Based on 6,369 DVSA MOT tests, the most common failure is brake hoses perished or damaged — at 35x the national fleet average. Other frequent failures include suspension joint dust cover missing or no longe... and suspension joint dust cover severely deteriorated.
Is the Audi S4 reliable based on MOT data?
The Audi S4 has 10 MOT failure categories above the fleet average. Specialists also flag water pump failure as a concern. A pre-purchase inspection and service history check are recommended.
What MOT failures should I expect at high mileage?
Above 100,000 miles, the Audi S4 most commonly fails on seat mounting fault and light unit fault. Under 60,000 miles, the main issues are suspension pin, bush or joint worn.
How do I check a Audi S4's MOT history?
Enter the registration number into our free car check above. You'll see every MOT test result, advisories and failures, mileage readings, write-off status, and finance checks.
MOT failure data sourced from DVSA bulk test records via data.gov.uk. Ratios compare this model's failure rate against the national fleet average. Known issues sourced from manufacturer bulletins, specialist workshops, and verified owner reports.