Audi A4 vs Mercedes-Benz C-Class: which is the better used buy?

On DVSA MOT records the Audi A4 and the Mercedes-Benz C-Class are level — 0.3 of a percentage point apart once you allow for the age of each fleet, which is too close to separate them. Choose on the fault patterns and running costs below rather than on reliability.

MOT first-time pass rate

Counted from DVSA’s anonymised MOT test records. “vs age-matched” compares each model against what the national fleet scores at the same age — the only fair better-or-worse number, because an older fleet fails more whatever its build quality.

Model	Pass rate	Age-matched national	Difference	Tests
Audi A4	77.3%	75%	+2.3	24,990
Mercedes-Benz C-Class	78.6%	76%	+2.6	37,418

Source: DVSA MOT Anonymised Data 2025 (Open Government Licence v3.0). National first-time pass rate 77.3%. Applies to Great Britain — Northern Ireland is tested by the DVA under a separate manual.

Audi A4

B9 (2015–2023) · D-segment executive saloon and Avant estate. One of the most popular used premium cars in the UK alongside the BMW 3 Series. Available as saloon and Avant estate. Key engines: 2.0 TFSI petrol (150–252 PS), 2.0 TDI diesel (136–190 PS), 35 TFSI mild hybrid (150 PS), 40 TFSI (190 PS), 40 TDI (204 PS).

The Audi A4 B9 is a premium, refined executive car with strong build quality, but it requires disciplined Audi specialist maintenance to keep running costs manageable. The 2.0 TDI diesel is reliable on motorway mileage but has documented timing belt (not chain) service requirements — belt failure on the B9 2.0 TDI is an engine-write-off event. The 2.0 TFSI mild hybrid (post-2019) is the better choice for mixed UK driving. Avoid any B9 A4 without full documented service history — Audi's repair costs are high and an unmaintained A4 can quickly become very expensive.

What goes wrong

2.0 TDI timing belt service (interference engine)critical
No audible warning — belt failure is sudden and catastrophic. Prevention through scheduled service is the only protection.
All B9 A4 2.0 TDI (2015–2023) · Audi recommended interval: every 80,000 miles or 4 years (whichever first). Many specialists recommend 55,000 miles or 4 years in UK stop-start conditions. · £700–£1,200 timing belt kit (preventive); £8,000–£15,000+ engine replacement if belt fails (the 2.0 TDI is an interference engine — belt failure destroys the engine)
Check: Ask for documented timing belt replacement history. If the car is at 55,000+ miles with no record of a belt change, factor the service into the purchase price or walk away. The 2.0 TDI's timing belt is one of the most important pre-purchase checks on any B9 A4. The petrol TFSI engines use a timing chain — this concern is diesel-specific.
MMI infotainment and virtual cockpit freezingminor
MMI screen freeze; navigation crash; virtual cockpit going blank; MMI reboot loops
2015–2019 (older MMI generations) · Not mileage-related — software degradation over time · £0 — software update at Audi dealer; hardware replacement £600–£1,200 if MMI control unit fails
Check: Test all MMI functions during the test drive — navigation, Bluetooth, media, climate control (which is MMI-integrated on many trims). Ask if the latest Audi software update has been applied. Most MMI issues are software-related and resolved by an update.
S-Tronic DSG dual-clutch juddermajor
Shudder or hesitation when pulling away from standstill; jerky low-speed changes; clutch grab in first gear
2015–2021 (7-speed S-Tronic DL382/DQ381 automatic) · Above 35,000 miles in urban use; can appear earlier without service · £400–£700 DSG fluid and filter change + software calibration; £1,500–£3,500 mechatronic or clutch pack replacement
Check: Test the S-Tronic at walking pace in traffic and pulling away on a slope. Any shudder is the known Audi/VAG DSG judder. Ask for DSG service history — fluid change every 35,000 miles is the minimum. An unmaintained S-Tronic above 60,000 miles is a significant risk.
High-pressure fuel pump failure (2.0 TFSI EA888)major
Hard starting; rough idle; fuel pressure warning; misfires
2015–2019 (EA888 Gen 3 TFSI) · Above 60,000 miles · £600–£1,200 high-pressure fuel pump; £200–£400 low-pressure fuel pump
Check: Test cold start behaviour. Any hesitation or extended cranking before starting suggests fuel system issues. Ask about any fuel pressure warning codes in the service history.

Typical asking price:: B9 2015–2018 2.0 TDI: £8,000–£16,000 | B9 2019–2021 facelift: £15,000–£26,000 | Avant estate: £1,000–£2,500 premium over saloon
Real-world economy:: 49–57 mpg (2.0 TDI real-world UK motorway mixed); 38–47 mpg (35 TFSI MHEV real-world)
Vehicle tax:: £200/year standard rate from the second year, hybrids included — the alternative-fuel discount ended on 1 April 2025. Cars registered 2001–2017 pay a CO2 band, roughly £20–£790/year (2026/27 rates).
Best years:: 2019, 2020, 2021
Years to avoid:: 2015, 2016

Full A4 fault guide Used Audis

Mercedes-Benz C-Class

W205 (2014–2021) / W206 (2021–present) · D-segment executive saloon, estate (T-Model), and coupe (C205). Direct competitor to BMW 3 Series and Audi A4. Available with petrol (C180, C200, C300), diesel (C200d, C220d, C300d), and PHEV (C300e/de) engines. One of the most popular used premium cars in the UK.

The Mercedes C-Class W205 is a beautifully built executive car but has a significantly higher incidence of electrical faults, AIRMATIC suspension issues, and engine oil leak problems than the BMW 3 Series or Audi A4 at comparable mileage. The M274 engine (C200, C250) had documented timing chain issues pre-2016. The OM651 diesel (C220 CDI pre-2016) had oil leaks and high-pressure pump failures. The W205 C-Class requires a good independent Mercedes specialist to keep running costs manageable — main dealer servicing is expensive. The post-2019 facelift is significantly more reliable than launch cars.

What goes wrong

M274 engine timing chain (C200/C250 petrol, pre-2016)critical
Rattling on cold start from the rear of the engine; timing-related engine management codes; rough running
W205 2014–2016 with M274 engine (C180, C200, C250) · From 50,000 miles; higher risk above 60,000 miles · £1,500–£3,500 timing chain replacement; more if engine damage has occurred
Check: Listen for chain rattle on cold start. Check the service history for evidence of the M274 updated timing chain tensioner being applied. Post-2016 W205 models use the updated M274 specification — significantly lower risk.
AIRMATIC suspension failure (C-Class with AIRMATIC option)major
"Car too low" warning; suspension compressor noise; car sits unevenly; ride height varies after standing overnight
2014–2021 (W205 with AIRMATIC air suspension option) · From 50,000 miles; risk increases with age (rubber bladders degrade) · £600–£1,200 per air strut; £400–£800 compressor; £200–£400 ride height sensors
Check: Check whether the car has AIRMATIC air suspension or conventional coil springs (AMG Line and higher trims are more commonly AIRMATIC). If AIRMATIC: walk around the car on level ground and check it sits evenly. Listen for compressor noise on startup. AIRMATIC repairs are one of the highest-cost common fault areas on used W205s. Cars with conventional springs avoid this entirely.
7G-Tronic Plus automatic gearbox valve body faultsmajor
Jerky or hesitant gear changes; gearbox warning light; car stuck in one gear; delayed response from standstill
2014–2018 (7G-Tronic Plus) · Above 50,000 miles; can appear earlier without service · £600–£1,200 valve body replacement; £300–£500 gearbox fluid and filter service
Check: Test all gear ranges on the test drive, including manual mode paddle-shift. Any hesitation or warning lights require investigation. The 7G-Tronic Plus valve body is a known wear item on high-mileage W205s without regular gearbox servicing.
Oil leaks (OM651 diesel, C220 CDI pre-2016)moderate
Oil visible on engine underside; oil smell when stationary; oil level dropping between services
2014–2016 (C220 CDI with OM651 diesel) · Above 60,000 miles · £300–£800 turbo oil feed pipe seal; rocker cover gasket £200–£400
Check: Check the underside of the engine during a pre-purchase inspection for oil residue — especially around the turbocharger oil feed pipe and rocker cover. OM651 oil leaks are a documented weakness on high-mileage cars.

Typical asking price:: W205 2015–2018 C220d: £9,000–£16,000 | W205 2019–2021 facelift: £15,000–£24,000 | C300e PHEV: £18,000–£27,000
Real-world economy:: 49–57 mpg (C220d real-world UK motorway); 38–44 mpg (C200 petrol real-world)
Vehicle tax:: £200/year standard rate from the second year, hybrids included — the alternative-fuel discount ended on 1 April 2025. Cars registered 2001–2017 pay a CO2 band, roughly £20–£790/year (2026/27 rates).
Best years:: 2019, 2020, 2021
Years to avoid:: 2014, 2015, 2016

Full C-Class fault guide Used Mercedes-Benzs

Which one suits you

Audi A4

Good for: Executive-segment buyers who want a refined, well-built premium saloon or estate. Motorway commuters (A4 Avant TDI is excellent value for high-mileage motorway use). Buyers who will use an Audi specialist for servicing.

Less good for: Buyers who cannot verify the 2.0 TDI timing belt service history. S-Tronic automatic buyers without DSG service history above 35,000 miles. Buyers wanting the lowest total cost of ownership — a Skoda Superb or Skoda Octavia diesel estate offers broadly similar space and refinement for significantly lower running costs.

Mercedes-Benz C-Class

Good for: Buyers who want Mercedes-Benz prestige and build quality and will use a specialist for servicing. Post-2019 W205 facelift buyers with documented service history. C300e PHEV buyers with home charging who want a premium PHEV at this price point.

Less good for: Buyers looking for the lowest total cost of ownership in the executive segment — the BMW 3 Series and Audi A4 are less expensive to maintain. W205 2014–2016 buyers without verified timing chain history on M274 engines. Cars with AIRMATIC suspension without recent AIRMATIC service history.

Frequently Asked Questions

Which is more reliable, the Audi A4 or the Mercedes-Benz C-Class?

Neither, on the evidence. Their first-time MOT pass rates sit 0.3 of a percentage point apart once each is compared against the national rate for cars of the same age, which is inside the noise. Pick on the specific faults each is prone to instead.

What is the MOT pass rate for the Audi A4?

77.3% of Audi A4s pass their MOT first time, from 24,990 tests in DVSA's records. The national first-time rate is 77.3%, but cars of this model's age average 75% — so it runs 2.3 points better than its age group.

What is the MOT pass rate for the Mercedes-Benz C-Class?

78.6% of Mercedes-Benz C-Classs pass their MOT first time, from 37,418 tests. Against the 76% that cars of its age average, it runs 2.6 points better.

Which years should I avoid?

For the Audi A4, 2015–2016 B9 launch cars: more reported MMI infotainment issues, some ZF gearbox calibration complaints on early DSG/S-Tronic automatics, and earlier fuel system issues on the 2.0 TDI before production revisions. For the Mercedes-Benz C-Class, 2014–2016 launch cars: highest incidence of M274 timing chain issues, gearbox 7G-Tronic valve body problems, panoramic roof seal leaks, and electrical fault reports. The OM651 diesel used in early C220 CDI also had documented oil leaks from the turbo feed pipe.

Which is cheaper to run?

The Audi A4 returns 49–57 mpg (2.0 TDI real-world UK motorway mixed); 38–47 mpg (35 TFSI MHEV real-world) in real UK driving; the Mercedes-Benz C-Class returns 49–57 mpg (C220d real-world UK motorway); 38–44 mpg (C200 petrol real-world). Vehicle tax: A4 — £200/year standard rate from the second year, hybrids included — the alternative-fuel discount ended on 1 April 2025. Cars registered 2001–2017 pay a CO2 band, roughly £20–£790/year (2026/27 rates).; C-Class — £200/year standard rate from the second year, hybrids included — the alternative-fuel discount ended on 1 April 2025. Cars registered 2001–2017 pay a CO2 band, roughly £20–£790/year (2026/27 rates).. Insurance differs mainly by driver and postcode rather than by model, so treat any model-level insurance figure with caution.

MOT figures are counted from DVSA records and are the only measured statistic here. Prices, economy and tax bands are indicative and vary by specification, condition and where the car has lived. Last reviewed: 2026-08-14 / 2026-08-14.