The 2.0-litre TDI in the new A6 Ultra emits just 114g/km of CO2, making it drop a road tax bracket to Band C, and cutting £125 from the on-the-road price of the 2.0 TDI 177 S tronic model that it replaces.
Power and torque have both been increased, and this engine is paired with a tweaked version of the S tronic automatic gearbox, which is smoother and quieter than before.
The Ultra engines also meet the strict Euro 6 emissions regulations, which limit the amount of harmful NOx emissions that any diesel engines are allowed to produce.
It is available in both the saloon and Avant estate bodystyles, and in SE, S line and Black Edition trims; manual versions will be introduced later this year, designed to attract company buyers who might be considering a BMW 520d or Lexus GS300h.
What is the 2014 Audi A6 Ultra like to drive?
Excellent. The Audi A6 has always trailed the BMW 5 Series in dynamic ability, but this new Ultra engine is incredibly smooth and refined for a four-cylinder diesel. It’s so quiet, in fact, that you could easily be fooled into thinking it was the 3.0-litre V6 model.
Combine this class-leading engine refinement with the revised S tronic auto gearbox and the A6 Ultra becomes the ideal tool for tackling any long-distance motorway journey.
Leave the gearbox in auto mode and it changes gear smoothly, while the steering-wheel-mounted paddles offer the driver a greater level of control when required. The extra 12bhp and 15lb ft of torque on offer give greater in-gear flexibility and make the A6 surprisingly quick.
The engine stop/start system is effective, too, and there are no unwelcome judders or shakes to accompany each restart. The car we tried was in the sportier S line trim, which has a firmer ride than the standard car and it does feel a bit too stiff on some surfaces.
Speed bumps and potholes send a thud through the cabin, but wind and road noise are very well suppressed – even when pressing on.
One area where the A6 still lags behind its rivals, though, is the steering. It feels slow and lifeless, regardless of which setting you choose from the Dynamic Drive select menu, which adds weight but provides no extra sensation.
What is the 2014 Audi A6 Ultra like inside?
Audi often leads the way when it comes to interior quality, so even after three years on sale the A6 still feels surprisingly modern from behind the wheel.
There are quite a lot of buttons to contend with on the centre console but after learning where everything is, the MMI infotainment system is easy to navigate and the retractable screen is bright and clear.
Every A6 comes with leather seats, sat-nav, DAB radio and cruise control, which all help make it feel like a convincing premium package, and our car also came with a few choice extras from the options list, including heated seats (£300) and upgraded sat-nav (part of a £1500 pack that also includes a larger screen and upgraded Bluetooth).
The driving position is superb, with plenty of head- and shoulder-room, and a wide range of manual adjustment that makes it easy to find the right setting to suit drivers of all shapes and sizes. All the switchgear feels robust and the materials are still among the best in this class.
Things are a little more cramped in the rear seats, and taller passengers will feel their heads brushing the roof, but legroom is generous. The large (530-litre) boot can carry as much as 995 litres with the rear seats folded flat, although like most saloons, the boot opening is narrow, which restricts what you can carry.
Should I buy one?
Quite possibly. The A6 Ultra is a fantastic addition to the A6 range and any company car driver covering high annual mileages will be impressed with its blend of efficiency, refinement and effortless in-gear pace.
The Lexus GS300h is slightly cheaper to run as a company car, but the Audi has the edge when it comes to practicality and interior quality, and its diesel engine promises to squeeze a few more miles out of every gallon of fuel.
Those looking for thrills from behind the wheel are still better off with the sharper-driving BMW 520d, because the A6's less settled ride and vague steering let it down in this area, but this new Ultra version has really helped close the gap between Audi and its executive car rivals.
What Car? says...
2.0 TDI S tronic
Engine size 2.0-litre diesel
Price from £32,515
Torque 295lb ft
0-62mph 8.2 seconds
Top speed 144mph
Fuel economy 64.2mpg