Cylinder deactivation disable

Several V8 and W12 engines shut down half their cylinders at a cruise. Audi call it
Cylinder on Demand, Mercedes have it on the AMG 4.0, Bentley and Lamborghini share the Audi
system, Porsche have it on the 4.0 V8. Under light load four cylinders go quiet, the other
four work a little harder, and the car sips fuel on the motorway.

Why people switch it off

Two reasons come up. The first is feel: the transition in and out of four-cylinder mode is
not always seamless, and some owners feel a shudder or hear a change in note they never get
used to. The second is wear: on some engines the deactivated cylinders run cooler and the
valvetrain that switches them adds complexity, and a proportion of owners of high-mileage cars
would simply rather it was not happening.

What the calibration does

The engine runs on all eight all the time. Fuel economy at a steady cruise drops by a
noticeable margin – this is a system that works, and turning it off costs something. Nothing
else changes: power, torque and emissions equipment are exactly as they were.

It is worth saying that we do not recommend this for every owner. If your car has the
system working smoothly and you do a lot of motorway miles, leave it alone. It is for the
owner who has decided the trade-off is worth it.

For the trade

This is one of the jobs available through our dealer file service. Send the
original read, tell us the vehicle and what you need, and the file comes back
checked. If a job carries mechanical conditions on the car, they are listed in the
coverage table below and they apply to your customer’s vehicle too.

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