This is supposed to reset the Gearbox Adaptive Settings....
The Gearbox learns two main things...one is how you drive and the other is the wear and slack in the drive clutches.
The first: As you drive, you tend to make similar traits like how hard you accelerate or how quickly you brake, what the main road types you drive on, etc. The Gearbox ECU 'learns' the way you drive and can adapt gear change points and selects a more appropriate gear at a given point that matches as best it can your driving habits!
The Second: The gearbox adjusts hydraulic pressure and modulation to the drive clutches based on their level of wear and slippage...over time the clutch plates wear and more hydraulic pressure is required to stop them from slipping and also it takes longer for them to engage as the clutch piston has further to travel (I know it is fractions of mm's but it still takes a little longer for the clutch to fully engage the gear) the gearbox measures the slippage and how much pressure the clutch is requiring (through PWM of the Solenoid valve) and adapts its settings to ensure correct and complete clutch engagement.
With new fluid which has better characteristics than the old fluid, this *can* change the hydraulic clutch engagement settings the gearbox ECU has learnt over a period of time with old fluid...the new fluid in effect confuses the ECU.
Not sure if the above 'trick' works to reset the gearbox adaptions, as I tried it and didn't really notice any significant difference...I do know gearbox adaptions can be reset using diagnostics on the BMW's the L322 is based on...
My L322 (Petrol) takes a second or so to engage drive.....selct D and you then get a slight pause and then the car dips as drive is taken up then off you go....generally you don't get this pause on the P38's as the initial selection of drive gear is mechanical and not hydraulic like the L322's
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