06
You cannot change anything.
It's primarily the software and not transferrable to an 05 and ESPECIALLY an 04 which has a totally different electrical system!
so FORGET IT, it cannot be done
It's a check valve in the hydraulic system of the Haldex AOC that keeps the clutch pack "pressurized" so that it reacts more quickly.
Honestly, I don't think it's that big of an upgrade. You'd have to change the whole Haldex and as JRL says, it's likely that it would not be backwards compatible with the electrical system, especially going back to an '04.
And I am pretty sure it's not just a matter of harnesses, it's the actual CANBUS.
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