Models
4dr Saloon / 5dr Estate (3.0 TDI))
History
The S4 has quite an interesting history. By 2019, it had been a fixture in Audi's range since 1991, but S4s had only actually been based on the A4 body shape since 1997. Following that date, every generation version of this model was made available as a saloon or Avant (estate), but Audi continually changed its mind about the kind of engine this S model should have.
A 265PS 2.7-litre twin-turbo V6 was used in the 'B5'-series model that sold until 2003. Then 'B6' and 'B7'-series models fitted with a 344PS 4.2-litre V8-engine took up the baton until 2009, when a 333PS supercharged 3.0-litre V6-engined 'B8'-series design arrived. That car sold until 2017 when it was replaced by a 'B9'-series car that also used a 3.0-litre V6, though this time, it was turbocharged rather than supercharged and put out 354PS. Then in 2019, that 'B9'-series model was re-fitted beneath the bonnet with the mild hybrid 3.0-litre TDI diesel unit that features on the car we're going to look at here.
The one main thing that all previous S4 models have shared is discreetness. Unlike some rivals, this Audi has never shouted about the level of performance it offers. There might be extra exhaust pipes, subtle badging and some attractive alloy wheels, but Ingolstadt has always avoided bulging arches, vents and in your face body kits. And so we come to consider this post-2019-era S4 TDI model. It was a brave step to fit it out with diesel power. How does this version stack up to its predecessors? The S5 TDI sold until late 2023 and wasn't replaced.
What You Get
To look at this S4 model externally, you'd be hard pushed to know how potent it is. The Singleframe grille comes in 'S'-specific form and features a Twilight grey matt finish and dual aluminium struts, plus there's an S4-specific bumper.
From the side, you'll notice the traditional aluminium-look mirror housings, plus the big 19-inch wheels. And perhaps you might pick up the fact that this S4 has sports suspension that makes it 23mm closer to the ground than a normal B9-series A4. The Avant estate model measures in at the same length as the alternative saloon - just under 4.8-metres - but is 29mm taller.
At the back, S4-specific giveaways include an 'S' rear diffuser in Twilight grey matt, an 'S' rear spoiler and 'S'-specific dual-branch tailpipes, with twin oval pipes on the left and the right. Under the skin, there's the same stiff, sophisticated 'MLB Evo' platform that all modern Volkswagen Group models of this size from this period were built upon.
The exterior may be very much an evolution of previous generation S4 models, but the interior is a lot more avant garde. There's a flat bottomed S4-badged leather-stitched steering wheel, matt brushed aluminium inlays for various trim pieces and predominantly black fabrics and trim everywhere else. And there are 'S' Super Sports seats in Nappa leather that hold the driver tighter than a regular seat. They also have a massage function too, plus they're heated and electrically-adjustable.
The 12.3-inch Audi Virtual Cockpit instrument binnacle screen was standard. As was a 10.1-inch MMI Navigation Plus with MMI Touch infotainment package. It incorporates 3D navigation, voice control, a 10-speaker Audi Sound System, a DAB tuner and a range of Audi Connect Infotainment Services.
Take a seat in the rear and two adults will be very comfortable: a trio of folk less so. That's partly because of the centre transmission tunnel which is strangely prominent for what is, after all, primarily a front wheel drive model. Out back, there's a 505-litre boot in the Avant model (it'd be 480-litres in an S4 saloon). Use the sidewall catches to push forward the 40:20:40-split rear backrest and you'll free up 1,510-litres of space.
What to Look For
Most owners in our survey seemed happy. We've heard of gearbox problems, seat backrest faults and suspension issues, so check all these on your test drive. The steering rack can experience electrical and mechanical failure and might be noisy too. The most reported faults related to interior trim and non-engine electricals. Look out for bodywork scrapes and kerb damage to the large alloys. We've had some reports of issues with wear to the side bolsters of the leather seats, as well as squeaking front brake pads, so it's worth looking out for both of those. There were a few issues with the car's infotainment system, with phones not connecting properly and flickering screens being the main problem. Rattling parcel shelves and buzzing interior trims were also reported. The DSG automatic gearbox should be checked to make sure it's had a regular oil and filter change, as should the quattro four-wheel-drive system.
Many S4s will have been company or lease cars and, as a result, you should check the condition of the bodywork carefully. The high-quality fit and finish of an S4 also makes it an ideal candidate for clocking, so ensure the history is absolutely verified.
Replacement Parts
(approx based on an S4 2019 30 TDI - Ex Vat - autodoc.co.uk) An oil filter costs in the £4-£15 bracket. An air filter's in the £13-£20 bracket. Front brake pads sit in the £28 to £71 bracket for a set; for a rear set, it's around £20-£43. Front brake discs sit in the £41-£78 bracket; for a rear pair, you're looking at around £40-£65. Starter motor prices vary widely - from £55-£413, depending on brand. As do costs for an alternator (anywhere in the £186-£687 bracket we found).
On the Road
The switch to diesel was clearly the headline here - and quite a TDI unit it is, with mild hybrid electrical tech and prodigious pulling power - there's 700Nm of torque, 200Nm more than the previous 3.0-litre turbo petrol unit could muster. So much more grunt, which amply compensates for a marginal drop in power over that previous petrol powerplant - there's a 347PS total output, down from 354PS. That's good enough to get this car from rest to 62mph in just 4.8s, which is only a tenth slower than the previous 3.0-litre TFSI V6 petrol variant could manage. Top speed, as before, was artificially pegged at 155mph.
The TDI engine utilises a large turbo, which is partly driven by a little electric compressor, as well as exhaust gases. Audi claims that this set-up minimises the effects of turbo lag, with the system being automatically activated whenever the requested engine load exceeds the capabilities of the turbocharger.
But it's a diesel. Is that an issue when it comes to the all-important noise a powerful mid-sized sporting model like this should make? It certainly sounds strange when you go full throttle, particularly if you've used the 'drive select' drive modes system's 'individual' menu to tailor the engine sound to the loudest 'pronounced' setting. Some will find the orchestral accompaniment deep-chested and satisfying. For others, the effect will be like a tractor on steroids; ultimately, it's a matter of personal perception.
Anyway, to go with this model's change of engine, Audi upgraded this car in a number of other areas, adding in Progressive steering, refining the sports suspension and incorporating a revised chassis platform, which controls the car's quattro 4WD system. The transmission remained an 8-speed Tiptronic auto unit, but this set-up's impressively quick-reacting and smooth. Not so good is the lowered 'S' Sports suspension, which will be rather over-firm for some, though some original owners chose to improve it by paying extra for a 'CDC' 'Continuous Damper Control' system.