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 SQ5 TDI.

Richard Lane

Road tester
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.

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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.

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