Audi A6 review - MPG, CO2 and running costs

Large executive cars like the Audi A6 are often driven by high-mileage drivers, and economy will be at the forefront of both fleet managers’ and private buyers’ minds.

Take the most powerful, 282bhp 50 TDI diesel engine. Despite being capable of a serious turn of speed, this officially returns up to 41.5mpg in the entry-level Sport trim, which is fairly respectable given the performance. However, even the car’s lowest CO2 emissions of 177g/km means business users will be liable for the highest Benefit-in-Kind (BiK) rate of 37%. and emits as little as 146g/km of CO2, in both Sport and S line trims. 

All of the TFSI engines are pricey to tax, too, as even the least polluting petrol-powered Audi A6’s CO2 emissions put in the second-highest 36 per cent BiK rate for the 2020/21 tax year. They also can’t match the diesels when it comes to fuel economy: the most frugal 40 TFSI version can return up to 39.8mpg, versus up to 37.2mpg for the 45 TFSI version and up to 34.9 for the V6-powered 55 TFSI cars.

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Figures for the 2.0-litre 40 TDI mean it's the cheapest conventionally-powered Audi A6 to run. It can return up to 52.3mpg and emits 141g/km in the most affordable Sport trim, meaning a BiK rate of 31% in the 2020/21 tax year. By far the most affordable Audi A6 to tax is the 50 TFSI e plug-in hybrid – thanks to its low CO2 emissions of 35g/km and electric-only range of up to 34 miles, it has a 2020/2021 BiK rate of 10%. The claimed 188.3mpg fuel economy is very good, too, though you’ll need to make the most of the electric range to get close to matching it in day-to-day driving. 

Road tax (VED) for the A6 will span two brackets. Models that cost under £40,000 - which at the moment is just the entry-level 40 TDI and 40 TFSI Sport versions - pay a flat annual rate of £150, while all models costing over £40,000 – including entry-level cars with options – will be hit with a supplement of £325 for five years. This kicks in during the second year of a car’s life, bringing your annual VED bill to £475 (or £465 for the plug-in hybrid version) a year from years two to six. First year VED rates remain CO2 based, and tend to be bundled into on-the-road prices.

One thing helping the A6’s efficiency is the fact all models other than the plug-in 50 TFSI e come with mild hybrid system, which comprises a belt alternator starter (BAS) and lithium-ion battery. The four-cylinder 40 TDI, 40 TFSI and 45 TFSI get a 12-volt system, while the six-cylinder 50 TDI and 55 TFSI come with 48-volt setups.

When coasting with your foot off the accelerator between 34-99mph, the 48-volt mild hybrid system fitted to six-cylinder cars allows the engine to switch off, saving fuel. Similarly, the start-stop function can activate at 13mph and below, allowing the car to glide to a stop with engine-off efficiency, before the engine restarts when sensors detect the car in front moving off. Audi claims the 40 TDI's 12-volt setup works on the same principle as the 48-volt system, but cautions its efficiency savings are "somewhat reduced".

On the performance-orientated side of things, the S6 is your best bet if you wish to retain a modicum of affordability at the pumps. In saloon form the S6’s diesel engine returns a claimed average of 40.4mpg – not bad considering the car’s power, size and weight – while emitting 184g/km of CO2.

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Insurance 

The 201bhp 2.0-litre diesel 40 TDI will be the cheapest A6 to insure, sitting in group 33 out of 50 regardless of whether you choose S line or Sport trim. This is a higher group than the slightly less powerful (187bhp and group 31) BMW 520d M Sport, but lower than the slightly more powerful (228bhp) 525d, which gets group 37 insurance. The A6 does better than the E-Class when it comes to insurance, though, with the 194bhp E220d sitting in group 35. 

Depreciation 

The Audi A6 has two factors that pull it in opposite directions: on the one hand, large executive saloons tend to lose value relatively savagely; yet on the other, Audis have a strong reputation for residual values. The A6 has residual values after three years in the 41-46 per cent range, which is similar to the BMW 5 Series, with the Mercedes E-Class and Jaguar XF both very marginally ahead.