Fourth-generation exec express is one of a new diesel-first S-branded breed

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It may be difficult to predict exactly how much appetite the UK’s sports saloon faithful currently has for the fast, diesel-engined four-door.

Some manufacturers clearly think it’s so meagre as to justify the early removal of derivatives and the cancellation of development programmes; some, but not all. And perhaps it’s appropriate that, having had such a significant hand in the scandal that did so much damage to the reputation of diesel engine technology back in 2015, Audi should now be the company doing what it can to restore that reputation.

I can see the rational sense in moving the S4 to a diesel engine, but I do miss the genuinely raw and bombastic V8s these cars used to have

As the Ingolstadt firm announced earlier in 2019, all future S-badged go-faster Audi models in Europe, bar one or two, are now to come with diesel engines intended to be equally big on torque and accessible for pace as they are fuel efficient and long striding in real-world use. Some, like the SQ-tagged performance SUVs, already were diesels, of course; but for Audi’s longer-lived and more celebrated quattro-driven sports saloons – one of which, in its latest guise, is this week’s test subject – that’s a major development.

So what will diesel power mean, exactly, for this heavily facelifted sixth-generation S4 aside from the addition of a TDI naming suffix?

The best way to sum it up in headline terms may be to record that it has as much torque as the maddest Mercedes-AMG C63 super-saloon – but it is also rated for better than 40mpg on the latest WLTP combined fuel economy lab tests, offers twice as many driven wheels as the Merc and yet can be bought for two-thirds of the price.

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Predictably, though, this new-groove, all-paw fast Audi relies on a very wide-ranging selection of the latest powertrain technologies to achieve what it does, which we’re about to lay out in detail.

The Audi S4 line-up at a glance

The S4 will still be available with a petrol engine in markets other than ours, but it’s a 342bhp V6 diesel or nothing in the UK. However, as before, there’s still a choice of saloon or Avant estate bodystyles. At present, the S4 TDI is available in both standard and Black Edition trim levels, although a range-topping Vorsprung model will join the line-up later this year.

Price £48,000 Power 342bhp Torque 516lb ft 0-60mph 4.6sec 30-70mph in fourth 5.2sec Fuel economy 29.1mpg CO2 emissions 164g/km 70-0mph 46.9m

What Car? New car buyer marketplace - Audi A4 saloon


Audi S4 TDI 2019 road test review - hero side

The wider Audi A4 range has had a fairly major overhaul as part of the mid-cycle facelift with which this S4 TDI arrives, with 12V mild-hybrid powertrain technology being applied across most engines and a pair of new lower-end diesel options being added to bolster the car’s appeal as a big-selling company car.

You can’t imagine the range-topping S4 TDI will be a hugely popular fleet option, diesel or otherwise, but then there’s plenty here to entice private buyers. Now the only A4 available in the UK with more than four cylinders, the S4 adopts a 2967cc V6 that’s notably different from Audi’s old BiTDI, which powered the last Audi SQ5 TDI.

Audi’s hexagonal grille gets squatter with this facelift, making the front end look wider. On the S4, honeycomb mesh replaces the horizontal grille bars of the old car

With one conventional exhaust-driven turbocharger and one electrically actuated compressor, plus a new 48V electrical architecture with an enlarged starter/generator motor driven by current from a lithium ion battery, the engine produces 342bhp at the tip of a fairly peaky-looking power curve.

Thankfully, the 516lb ft of torque the same engine makes, between 2500rpm and 3100rpm, ought to result in a decidedly unpeaky-feeling power delivery overall.

The new S4’s electrical system and starter/generator mean the hybrid powertrain can regenerate power at an impressive rate, too – at up to 8kW – which contributes to lab-tested WLTP combined fuel economy of up to 40.9mpg, depending on optional specification. Addressing the veracity of that claim will be as important as any performance indicator for this test – and we’ll get to that.

The S4 comes with an eight-speed automatic gearbox (other two-pedal A4s use a seven-speed dual-clutch gearbox) and permanent centre-diff-based four-wheel drive. Since Audi UK has elected, for now at least, not to offer the 45 TDI engine option that’s part of the A4 range in other markets, you might even say this is the only A4 with ‘proper quattro’ four-wheel drive (since quattro-branded versions of the lesser petrols and diesels get a more fuel-efficient clutch-based four-wheel-drive system instead). Meanwhile, you can have Audi’s electronically locking sport rear differential on your S4 TDI if you want maximum driveline purposefulness, but only as a feature of standard equipment on the top-of-the-line Vorsprung model, which will be made available later this year.

Having been ordered before UK specs were fully set, our test car may look like something of an anomaly to those particularly familiar with the S4’s online configurator. Technically, it was a standard S4 TDI, although since it had a few key mechanical features (adaptively damped sport suspension, quattro sport diff, matrix LED headlights) that will be only available to the public on a Vorsprung S4, its driving experience was probably more representative of that flagship variant than of the sub-£50k entry-level version.

That the car also had active variable-ratio Dynamic steering, which Audi UK is not offering at all, explains why we’ll keep our remarks about the S4’s steering more general than we would typically.


Audi S4 TDI 2019 road test review - cabin

Much like its exterior, the changes made to the S4’s cabin are relatively modest. Where the previous model placed great focus on a more minimal, clean approach to interior design that embraced the use of tactile, visually appealing materials, so, too, does this new version.

As such, polished chrome, glossy piano black and surprisingly tasteful carbonfibre elements are used liberally and to great effect and lend the S4’s cabin a sophisticated, modern ambience that feels very much in step with its elevated price.

The adoption of Audi’s latest infotainment set-up means the old MMI touchpad and ‘rotary commander’ have been removed. Many will miss it, as we did.

That Audi now offers a fully digital set of instruments and an enlarged 10.1in touchscreen infotainment system on even the most basic A4 will probably do more for sales of cars at a lower price point than that of the S4. Even on a £50,000 car, though, the new MMI Plus set-up is slick and ritzy enough to win compliments.

The touchscreen's installation allows Audi to do away with the rotary dial that controlled the previous system. In its place on the centre console, you now find an additional compact storage compartment, which complements the S4’s already abundant interior repositories well.

As a result of losing the rotary input device of the pre-facelift car, you interact with the system mostly via the touchscreen itself; and although the free-standing installation is easy to grab hold of with an outstretched arm while the car’s moving, it’s not the most solid-feeling of fittings, at least by Audi’s high standards.

Usability is marginally less good than we’ve found with Audi’s dual-screen set-up in its bigger models – although it’s far from bad and, since it diverts your gaze less far from the road, may even seem preferable to some.

The premium audio option is the same Bang & Olufsen 3D system as the pre-facelifted car had, coming as part of a £1395 upgrade pack. Our test car did without it but didn’t struggle for system power or clarity.

Leather-upholstered sports seats come as standard and provide good levels of support and adjustability. The impressive configurability of their bolsters meant that even the scrawnier members of the road test team weren’t left feeling lost in their chairs. That said, even with the seats in their lowest setting, there was a feeling among our testers that the Audi’s overall driving position isn’t quite as naturally sporting as that of the new BMW 3 Series, in that it leaves you perched fractionally higher than you might like.

With a wheelbase shorter than that of the latest 3 Series, the S4’s second row isn’t quite as spacious as that of its Munich-based rival, although it’d be a stretch to say it’s in any way uncomfortable. Our road test tape measure recorded a typical rear leg room figure of 700mm versus the BMW’s 780mm (the BMW’s advantage stemming chiefly from having the deeper front footwells) while head room stands at 900mm.

Adults of an average height should therefore find little to complain about although taller individuals may find that head and leg room are just a touch on the mean side.

The boot, meanwhile, has a seats-up capacity of 420 litres, making it smaller than that of both the BMW and the Mercedes-AMG C43 – both of which have 480-litre luggage compartments.


If the switch to diesel has left you concerned that the new S4 might be short of accelerative potency compared with its petrol-powered predecessors, worry not. This new S4 TDI is no damp squib. Audi’s claimed 0-62mph time of 4.8sec appears to be realistic or, if anything, a touch conservative. Even with its fuel tank brimmed and no launch control system in sight, our test car managed to hit 60mph from a standstill in 4.6sec.

More intriguing, however, is that the S4’s 0-60mph time not only beats that of the Audi 349bhp petrol-engined S5 Coupé we road tested in 2017 (4.9sec), but it also eclipses the 5.3sec time set by the Ford Mustang Bullitt (admittedly on a damp track) with its gargantuan 5.0-litre 453bhp V8. Of course, the deep, bassy grumble of the S4’s oil-burning V6 is nowhere near as characterful or appealing as the noise made by either of those petrol engines, but such a comparison highlights just how effective this new four-wheel-drive diesel performance car is judged strictly in terms of outright shove.

S4’s sure-footed four-wheel drive and disciplined body control instil considerable confidence in its driver, but you can provoke the tail to step briefly out of line if you want

With a C63 S-rivalling 516lb ft of torque on tap between 2500rpm and 3100rpm, its mid-range punch and overall flexibility are dramatic, too. Even with the crankshaft spinning at 2000rpm, you’re aware of sitting on an immense well of accelerative force, and as the revs rise towards 3000rpm, the tidal manner in which the S4 sucks you towards the horizon gets only more uncanny. Locked in fourth gear, the Audi was able to accelerate from 30mph to 70mph in 5.2sec – a whole second quicker than the old S5. Above 3500rpm, mind you, the car’s appetite for speed grows markedly less insatiable.

There are a few small flies in the ointment, though, the first concerning the eight-speed transmission. Even when supplemented by that 48V mild-hybrid architecture, it’s not quite as responsive to your inputs as you’d like. Part-throttle response is particularly unenthusiastic and it takes a proper shunt of the righthand pedal to initiate kickdown.

When you’re simply trying to pull away from the lights in a swift yet controlled manner, the S4’s almost binary reactions to your inputs don’t always make for the smoothest progress.

Less irritating are the brakes, which, while undoubtedly effective, feel a touch numb and over-assisted. At speed, you don’t really notice the immediacy with which a prod of the brake pedal will begin to slow the car, but around town, this lack of finesse can again act as an impediment to smooth progress.


Audi S4 TDI 2019 road test review - cornering rear

The S4 slips effortlessly into the dynamic space occupied by the vast majority of fast Audis: its quattro four-wheel-drive system, chassis and steering all work together to harmoniously, if a little coldheartedly, deliver a level of security, drivability and point-to-point pace – regardless of the prevailing weather conditions – that few rival performance saloons can match.

However, where many of its range mates maintain their sense of steely, overly serious determination at all costs, the S4 is capable of letting its guard down for brief moments. With its stability systems reduced and a heavy application of throttle on corner exit, fleeting instances of tail waggling can be coaxed out of the otherwise steadfastly inert S4.

V6 diesel engine’s immense torque reserves endow it with incline-levelling amounts of acceleration out of corners

The car doesn’t hold a candle to the new BMW M340i xDrive in terms of expressive adjustability (which, even in prototype form, proved a wieldy, highly engaging performance saloon), but even a modest sprinkling of dynamic liveliness is nonetheless welcome.

The S4’s steering, meanwhile, is direct but typically tight-lipped. With 2.25 turns between locks, it lends the Audi a suitably responsive front end, although it doesn’t bode particularly well for the S4’s ability to engage that the passive system fitted to UK cars should make for a slightly gentler and lighter-feeling tiller. For what it’s worth, the Dynamic set-up proved well weighted and as capable of filtering out bump steer and other corrupting influences as you’d expect of a modern fast Audi.

Body control is very good. Even with the S4’s adaptive dampers in their slackest setting, they kept lateral roll tidily and progressively checked and contributed to the sense of unerring confidence the S4 imparts when driven swiftly.

Driven hard on Millbrook’s challenging Hill Route, the S4 was seriously quick. The V6 diesel engine’s immense torque reserves endowed it with incline-levelling amounts of acceleration out of corners and the grip and stability afforded by its chassis allowed impressive speed to be carried through them, too.

Surprisingly, though, the S4 wasn’t so composed that it lacked a sense of humour. Backed into sharper bends on the brakes, it would willingly begin to rotate. The same effect could also be achieved by burying the throttle on the exit of the corner.

Even with the stability systems left on, progress around the circuit was fluid and unimpeded, with only the most severe compressions forcing them to step in and restrict progress. At pace, the Dynamic steering took a bit of time to acclimatise to, but once dialled in, the quickened response when travelling at pace proved entertaining.


Our S4 TDI was fitted with adaptively damped S sport suspension, which will be available on only forthcoming Vorsprung models in the UK. So equipped, there’s a noticeably firmer edge to the primary ride than you might expect, but this isn’t so pronounced as to make the car uncomfortable or taxing to drive.

Even in Comfort mode, there is a fairly stern air about the S4’s vertical body control that allows it to handle undulating surfaces in a manner that feels taut and purposeful but isn’t so unforgiving as to give the base of your spine much trouble. Secondary intrusions are felt moderately keenly when crossed at town speeds, but again the severity of such impacts doesn’t seem grossly out of step with what you’d expect from the average performance saloon. If anything, they surprise you only very slightly from an Audi S car.

Greater pace improves the S4’s ride and reinforces the impression that this is a car more suited to quickly dispatching vast distances on Britain’s motorways and dual carriageways than being thrashed down your favourite B-road. Combine this dynamic confidence with a comfortable driving position and a hushed, refined powertrain and the result is a formidable long-distance tourer.

Formidable but not quite perfect. While the engine is certainly demure at a cruise, the 19in alloy wheels and tyres do generate a noticeable amount of roar on Britain’s at times coarse road surfaces. At a sustained 70mph cruise, our sound gear measured cabin noise at 70dB.

Admittedly, that’s not terrible, but the 320d we road tested earlier this year (which ran on lowered M Sport suspension and 18in wheels) returned a reading of just 64dB in the same conditions.


Audi S4 TDI 2019 road test review - hero front

Many of the familiar arguments for buying a diesel-powered executive saloon don’t apply to the S4 TDI. The car’s relatively low CO2 emissions do help deliver a lower showroom price for the car than its petrol-powered opponents might have, thanks to relatively low first-year VED ‘showroom tax’ banding. The way that emissions-related company car tax bands are currently set, however, means those choosing the car as a fleet option won’t be rewarded with any less benefit-in-kind liability than they would have if they’d gone for a petrol-powered rival.

You’ll also need to pay for the fuel in your car’s tank out of your own pocket, rather than as a business expense, to see the sense in picking diesel over petrol on fuel economy grounds – and you’d imagine that plenty of potential S4 owners won’t.

Rivals for the diesel S4 are thin on the ground, but it performs competitively against the Mercedes-AMG C43 and BMW 330d xDrive M Sport.

However, those who do should be very pleasantly surprised by the fuel economy that the car’s capable of. A test average of only just under 30mpg for our car may seem underwhelming – but a touring test result of better than 50mpg, representative of the car being driven at a steady 70mph, is quite remarkable for a car of this size and performance level. At that economy, the S4 could put almost 700 miles between fills of its 58-litre tank.

What Car? New car buyer marketplace - Audi A4 saloon


Audi S4 TDI 2019 road test review - static side

So what sort of performance car is this new oil-burning S4? Previous incarnations haven’t always stood out as being the most involving driver’s cars but the shift that’s occurred here - which makes the S4 more of a devastatingly quick, refined and technologically advanced long-distance cruise missile than ever – seems well calculated.

Used thoughtfully, it’s a highly credible machine indeed. The S4’s cabin is easily up with the best in class for fit and finish; the diesel V6 is immensely potent and impressively refined and it can be remarkably frugal; and the car’s handling remains supremely secure, regardless of the conditions underfoot.

Diesel power sparks an appealing new identity for this fast Audi

That the S4 is still not the most expressive or engaging driver’s car will shock no one. But the repositioning that the introduction of diesel power has brought about seems to make this less of an issue than before. In fact, it shines a light on what looks to be a compelling new niche for the model. Some will lament the petrol S4’s European demise, but this new diesel model could well mark the start of an interesting new chapter for the compact, everyday-use, S express Audi.

What Car? New car buyer marketplace - Audi A4 saloon

Matt Saunders

Matt Saunders Autocar
Title: Road test editor

As Autocar’s chief car tester and reviewer, it’s Matt’s job to ensure the quality, objectivity, relevance and rigour of the entirety of Autocar’s reviews output, as well contributing a great many detailed road tests, group tests and drive reviews himself.

Matt has been an Autocar staffer since the autumn of 2003, and has been lucky enough to work alongside some of the magazine’s best-known writers and contributors over that time. He served as staff writer, features editor, assistant editor and digital editor, before joining the road test desk in 2011.

Since then he’s driven, measured, lap-timed, figured, and reported on cars as varied as the Bugatti Veyron, Rolls-Royce PhantomTesla RoadsterAriel Hipercar, Tata Nano, McLaren SennaRenault Twizy and Toyota Mirai. Among his wider personal highlights of the job have been covering Sebastien Loeb’s record-breaking run at Pikes Peak in 2013; doing 190mph on derestricted German autobahn in a Brabus Rocket; and driving McLaren’s legendary ‘XP5’ F1 prototype. His own car is a trusty Mazda CX-5.

Audi S4 First drives