Like its larger S6 TDI and S7 TDI counterparts, the Audi S4 has adopted a diesel engine – at least in the European market. Strange move? Perhaps, but with diesel still a popular choice in this segment it’s certainly a logical one.

It certainly did the larger cars no harm when we tested both a few months back, their 3-litre TDI engines providing plenty of power and torque and an unruffled delivery that suited each car down to the ground. Given the petrol S4 has rarely been the sharpest of tools, perhaps diesel can work well here too?

Engine, transmission and 0-100 time

The S4 TDI may be smaller than the recently introduced S6 and S7 TDI models, but Audi hasn’t held anything back with the S4’s 3-litre V6 TDI engine compared to its larger siblings. It develops the same 256kW at 3850rpm, and no less torque, with a massive 700Nm available between 2500 and 3100rpm.

Power is sent through an eight-speed Tiptronic automatic transmission and quattro all-wheel-drive system with self-locking centre diff, while our test car also featured Audi’s locking ‘Sport differential’ at the rear axle. In sedan form the S4 is capable of 0-100kmh in 4.8sec – two-tenths quicker than an S6 Avant and just a tenth shy of the old S4, despite a small horsepower deficit – while the S4 Avant is a tenth slower than the sedan. Both reach an electronically limited 250kmh.

As with the S6 and S7, Audi’s quoted fuel economy figures show only a small improvement over the petrol predecessor, but they’re also comparing apples with oranges. The new 5.7L/100kmh combined (5.9L/100kmh for the Avant) is recorded on the tougher and more realistic WLTP test rather than the old car’s 6.4L/100kmh on the NEDC test.

Technical highlights

Aside from the diesel engine, the S4 is the latest Audi to gain a 48V electrical system, mild hybrid technology, and an electric compressor to supplement the conventional turbocharger. The hybrid tech uses a belt-driven starter-alternator to allow for start-stop functionality and engine-off coasting, while the latter is said to improve throttle response.

As far as more visible technology goes, the latest S4, along with the rest of the A4 range, has adopted a 10.1-inch central touchscreen standing proud of the dashboard, with updates to the MMI interface and infotainment functions.

The interior design has changed less than the exterior, which LED headlights and tail lights aside, isn’t an entirely successful update to our eyes – the fake plastic urQuattro-aping trim above the grille and token blistered arches appear rather fussy.

What’s it like to drive?

Neither the S4’s revised styling nor its refreshed interior are likely to set the heart racing, and pressing the starter button to hear a diesel fire into life – even a diesel six – is unlikely to prickle the senses either. It must be said though, there’s character to the sound, and it’s hard to fault how effective the V6 is in this application.

Below around 2000rpm the engine isn’t overly enthusiastic, most easily discovered if you’re changing gear manually rather than leaving the ’box in auto. Proper electric torque-fill rather than half-hearted energy recuperation would be welcome here. But avoid the low-revs torpidity and ignore the last thousand rpm or so before the red line, and the S4 has real wallop. Overtaking is done in a flash and throttle response is impressive in that mid-range band, with an offbeat growl to the exhaust note.

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As with the larger S6 and S7, the unit also makes the S4 a fantastic cruiser, settling down to near-silence but always a quick downchange or two away from sprinting up to autobahn speeds. Top gear is tall enough that it’s overly keen to change down on motorway inclines, but whether you use the paddles or leave the transmission to its own devices, changes are always smooth and swift.

The same can be said of the S4’s cornering behaviour. Not yet a car you’d take out for a sunday morning blast, Audi’s chassis are nevertheless getting better and better. Dynamic steering is bordering on the likeable these days. It’s low on weight and feedback, but there’s plenty of precision, and combined with great body control and strong grip, it makes the S4 a very easy car to place.

S4s lack the S6 and S7’s rear-wheel steering so there are times when the smaller car actually feels a bit less wieldy than its heavier brethren, but throwing an Avant through a snaking series of turns, feeling the rear axle share the cornering load and the sport diff bolstering corner exit traction, is surprisingly good fun. And as a package – smooth, swift, composed and frugal – the S4 has perhaps never made more sense. ANTONY INGRAM