The picture
A4 Passes 76.6% — Diesels Carry the Hidden Cost
At an average test mileage of 105,387 — the highest of any car in this analysis — the Audi A4's 76.6% pass rate is reasonable but not exceptional. Worn tyres and fractured springs are the most common failure causes. Dig deeper and diesel running costs mount quickly: EGR failure on a 2015 2.0 TDI ran to £1,500 at 60,000 miles, while an AdBlue module control unit on a 2016 Avant Ultra came in at £930.
Infotainment glitches on newer models are a nuisance rather than a structural problem, but the pattern of diesel-specific component failure is worth factoring into any ownership calculation. A full service history and confirmed EGR and AdBlue system health are non-negotiable checks for any used A4 TDI.
Top ten reasons for rejection.
- 01
Tyre tread depth not in accordance with the requirements
12,082 occurrences · 3.8% of tests
- 02
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
12,004 occurrences · 3.7% of tests
- 03
A spring or spring component fractured or seriously weakened
10,888 occurrences · 3.4% of tests
- 04
A rear registration plate lamp or light source missing or inoperative in the case of multiple lamps or light sources
10,701 occurrences · 3.3% of tests
- 05
A transmission shaft constant velocity joint boot severely deteriorated
9,391 occurrences · 2.9% of tests
- 06
A suspension joint dust cover severely deteriorated
7,868 occurrences · 2.5% of tests
- 07
A suspension pin, bush or joint excessively worn
7,825 occurrences · 2.4% of tests
- 08
A transmission shaft constant velocity joint boot missing or no longer prevents the ingress of dirt etc
7,800 occurrences · 2.4% of tests
- 09
A tyre cords visible or damaged
5,277 occurrences · 1.6% of tests
- 10
a brake lining or pad worn below 1.5mm
4,865 occurrences · 1.5% of tests
Counts cover Major and Dangerous defects logged at test. Advisory items excluded so this shows why a car was rejected, not just what the tester flagged in passing.
Worst-case fix budget · top 3 failures
£148–£370
If every one of this A4's most-logged Major fails hit at the same MOT, that's the real-world UK garage range. Reality is usually one or two items, not all of them. Open the estimator →
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Tools that pre-empt a retest.
Picked against this car's top failure patterns. Affiliate links to Amazon UK — we earn a small cut at no cost to you. Disclosed up-front, doesn't shape the data.
Item 01 · Amazon UK
Digital tyre-tread depth gauge
Five quid for a gauge beats £150 for a retest. UK MOT minimum is 1.6mm — most testers fail anything below 2mm to be safe.
Search Amazon UK
Item 02 · Amazon UK
H7 / W21W bulb pack
A spare-bulb kit lives in the boot. Test morning is not the time to find your stop-lamp's gone.
Search Amazon UK
Owner reports · Honest John
What owners actually report.
Verbatim faults logged by owners on honestjohn.co.uk over recent years. We didn't summarise — these are the words people typed in.
What's good
Exceptional quality, packed with technology, impressive refinement and comfort, efficient and economical.
Recent owner-reported faults
- 7 May 2021
Adblue module control unit failure reported on 2016 Audi A4 Avant Ultra 2.0 TDI. Owner quoted £930 to replace the unit.
- 23 Mar 2020
Owners of three month old car reports problems with the infotainment system. When they get in the car and drive off an error message often comes up saying "The selected user has not been used in this vehicle for a while. Please enter the MyAudi user data again. It will be necessary to switch to the guest user to do this." Local dealer has told the owners that Audi UK are aware of the fault and they are awaiting a software fix from Audi Germany.
- 20 Dec 2019
Report of failure of EGR on 2015 Audi A4 B9 EA288 2.0TDI at 60,000 miles. Cost of replacement was £1,500.
- 29 Nov 2019
Report of "persistent vibrations coming through the accelerator pedal and the steering wheel, often simultaneously" in November 2015 Audi A4 B9 avant 8-speed auto, 3.0 TDI V6 272HP. Has had replacement of several expensive parts under guarantee due to factory recalls (4 camshafts, crank shaft, chain tensioner), but problem's remains. In D the vibrations arrive around 1,250 rpm especially when accelerating. Owner notices that despite regular cleaning and quality fuel all the time, the engine is also quite noisy when accelerating: "it's as if there's a part somewhere which is noisier than it should be and injects vibrations into the mix when increasing speed." Also, when the car is hot and in traffic it can start to tremble slightly until shifted into Neutral. If driver leaves car in S in traffic, the vibrations are slightly stronger still.
- 31 Jul 2019
Owner found that the 19-inch optional alloy wheels fitted to his March 2017 Audi A4 2.0TDI quattro s-tronic s-line had increased its CO2 from 114g/km to 121g/km and put up his annual VED from £30 to £120.
- 16 Feb 2019
Complaint of "soft knocking sound around driver's right ear" when driving on a "roughish road surface" in a new Audi A4 B9. Seems to be from an area around drivers window/door lock/door pillar. Likely to be the inertia reel seatbelt pendulum.
- 28 Dec 2018
Report of vibration from drivetrain of November 2018 Audi A4 B9 avant 272 3.0 V6 now at 45k miles: At 1,250 rpm, whether in D or S mode, there is vibration which passes through the accelerator pedal and steering wheel. Also at 1,750 rpm when cruising on the motorway at 80 mph with cruise control on in 8th gear it doesn't feel as smooth as it should. Finally, when around 2,000 rpm the car feels unrefined and actually noisy for an Audi V6 diesel.
- 7 Aug 2018
Audi dealer told owner that intermittent shudder in 1st gear when releasing the clutch of his 2016 Audi A4 may be due to "driver error" that has damaged the dual mass flywheel and want £1400 to "investigate" (this must include the costs of a new DMF and clutch).
- 9 Jul 2018
Report of two failed transmissions on 2015 Audi S4 in 25,000 miles. Unfortunately owner failed to renew extended warranty.
- 15 Jan 2018
Various niggling problems reported with June 2016 Audi A4 B9. In May 2017 the car failed twice, on consecutive days, and the Engine Management Unit was replaced. At the same time owner advised the dealer that the electronic dipstick was reporting the engine oil level as being at full capacity although he had not topped up the oil, that the trip odometer and the long term memory were intermittently clearing to zero and the external thermometer was occasionally displaying obviously faulty temperatures. In July 2017 he again reported to the dealer the potential problems with the electronic dipstick and the other display issues. He was simply told that "new cars don't use oil". The engine oil has not been topped up since first delivery. The trip odometer and long term memory inexplicably reset to zero yesterday.
- 18 Aug 2017
Report that on 4th August a 7 month old 2017 Audi A4 Avant came to a sudden halt from 38mph for no reason, on a clear road, causing the following car to crash into the back of it.
Source: honestjohn.co.uk · 11 reports indexed
Buying or keeping a A4?
Use the failure ranking as a pre-test checklist or a haggling lever. Treat the headline pass rate as a fleet-wide trend, not a guarantee on any individual car.
If you own a A4 and your last MOT looked nothing like the ranked failures above, that's normal — individual cars vary widely. The ranking shows the patterns testers flag most often across the country.