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The most misunderstood part of transmission control

Since the launch of xHP, nearly 1 year ago, there is the same question popping up every week by customers: “Does xHP reset my transmissions adaptions when flashing?” To cut that short: No, xHP does not reset adaptions and they do not get reset, when flashing the transmission at all. That means, they do not get reset at the dealer either, when you are there for an update. And there are good reasons for it.

First, let’s have a look what Adaptions are and what they are good for. Adaptions basically have two purposes. The very first is to overlay the basic maps, stored in the TCU, by some small offset maps to compensate mechanical/hydraulical tolerances. No transmission is 100% identical to the other in real life and those differences need to be kept in check. So, the aim is to correct the errors in the stored basic setting, if you will.

Secondly, every moving part inside the transmission will wear over it’s lifetime. This is especially true for the clutch packs, which are built to wear by nature. Just like your brake discs wear through friction between disc and pads, so do your clutches (there are 5 of them in the 6HP + the Torque Converter Clutch) on every shift. Don’t panic, most of that wear is controlled through the lubrication with the transmissions oil. That also explains, why oil changes approx. every 60.000 miles are not the worst idea, despite BMW not recommending them. Normally the 6HP’s clutches are good for 200.000 miles and much more. Wear of clutch packs means, they get thinner and thinner over their lifetime.

This leads to the conclusion, the transmission controller has to have a function, to compensate this. Those are the Quickcharge Times and Quickcharge Pressures. They are there to compensate the higher travel, the piston needs to actuate the clutch, before it starts to bite. This is the same principle, employed by your brake system and employed by a manual clutch to compensate for wear. It’s more complicated in the transmission, but the logic is the same.

So, with that knowledge, what is it good for to reset adaptions regularly? Simple answer: For nothing. In rare cases, on transmissions with already very high positive adaptions, this can even lead to a situation, where your transmission will refuse to shift and you basically have to rebuild it, before it will work again. And that is the reason, why adaptions do not get reset by the dealer on service work. There is no reasons for it, unless hardware on the transmission has been changed.

Below you can see how typical (basic) adaption values look like on a 335i car with around 60.000 miles on it. Common min./max. values are -+400 mbar for the Pressure adaption and +-40 ms for the Quickcharge Times. Values above or below are treated as “out of tolerance” but however, transmission can still run and shift "normally" with + 700 mbar as well.