This is a way of cutting the ignition and fuel to the engine so you can crank to prime the oil gallery prior to starting.
Why do this? If you have done any engine work, the car has sat for a while without starting, or most commonly after an oil change. Changing the oil filter will empty the oil filter housing, so priming the system will have it fully lubricated immediately on start rather than having no oil pressure for the first few seconds with the associated metal on metal rattling.
First thing is to shutdown the engine by pulling the fuel pump fuse. The engine will stop within a few seconds. Leave the fuse out. Fuel pump fuse is B5 on the left footwell panel. Tool to remove fuses is in the right footwell panel. Image below of fuse location. Note this is an approved procedure in the workshop manual to shutdown the engine and remove the fuel pressure from the fuel system.
When you complete your work, and you intend to start the engine, remove the ignition fuse in the right rear part of the boot/trunk. You don’t need to remove the lining, just pull it back to expose the fuse panel and remove the fuse shown below. This is the circuit that provides high power to the spark plugs. The signal from the ECU for spark plug firing will still occur, but the high power source to create the spark will not be available.
When you now crank the engine, the spark plugs won’t fire and there will be no fuel injected.
Turn the key like you are trying to start the car. It will crank for about 5 seconds prior to it stopping on its own. Turn key to off and do it again. I normally do this twice (about 10 secs or cranking) for a simple oil change to ensure the oil gallery is full. If you were doing an engine rebuild, a lot more would be required. You should hear a small increase in RPM when cranking when oil is finally everywhere.
Now replace both fuses. When starting the car, turn the key to the first position for a few seconds (this will prime the fuel system) and then turn the key to start. It should start with no unusual noises. No codes should be recorded in the ECU.
I did this on my recent oil change and was very happy with the softness of the start. It was like it had been shutdown only moments earlier.