Actually on a 722.9 the TCM is embedded in the conductor plate along with a couple of internal speed sensors the connections to which can be repaired if that is the failure mode. Not a good environment for sensitive electronics bathed in hot fluid.
Usually the failure mode is either one or two speed sensors or everything goes wonky when the TCM fails. In that case you get nothing on a scan but a bunch of solenoid codes. There are some outfits that can repair the sensors issue. For everything else you can gamble on a used CP or buy a virginized CP. These need to be programmed/cloned to the car which depending on how you deal with can be $0-$400. The ISM ( a stupid idea for a motorized shift motor that selects P R N D) can also fail and it is also programmed to the car. One of those is like $300 off eBay or again a used one might work. All these bits talk to one another. ISMs can be a real PITA to swap depending on the car. On my S550 4matic the first instruction is “remove transmission.” There is zero room to get it off. It was doable on the ML by removing the front driveshaft and rear transmission mount then pulling it over with a come-along. This gave me about 1 inch to get it off. I have gotten pretty good at swapping CPs and I have a buddy who can do the cloning but unfortunately he is indisposed at present. I have my ML63 sitting at his shop waiting for a new CP to be cloned. (I also replaced the ISM, the original CP was probably OK but for reasons I don’t now recall I pulled it and broke it hence the need for the new one). When he becomes available again I’m going to get him to show me how to do the cloning on both bits. You need a special box to talk to the fancy computer and connect to the CP or ISM and have to go way down the vendiamo rathole into the controller but it’s pretty straightforward once you see it done. I see cars like this and for maybe a few $100 I could get them sorted with not a lot of hours invested and flip them or drive them. --FT Sent from iFōn > On Jun 12, 2024, at 5:42 PM, Jim Cathey via Mercedes <mercedes@okiebenz.com> > wrote: > > >> >> what is the failure mechanism of all these conductor plates? It seems to be >> so common. > > The Duh answer is: bad connections. I say Duh, because those plates are > essentially > nothing _but_ connections. The two speed sensors are just coils of wire, so > if one opens > up... bad connection! The solenoids are separately replaceable, the plate > part is > just: connections. Connections that live in a hot vibrating oil bath, how is > THAT a > good idea? :-) > > With electronics, once they figured out how to make durable silicon and the > like, > which they didn't always know how to do wrt electro-migration and poisoning, > if it didn't smoke (silicon, mostly) or dry out (capacitors), if it stopped > working it's > due to a bad connection. Somewhere. > > Similar to a mechanical adding machine. 99% of the failures are lubrication > failures. > Not that knowing this really helps you very much. There are a LOT of > lubrication points > in something like a rotary calculator, and there are a LOT of connections in > electronics. > > It does not help that modern construction uses smaller traces than necessary > for > low-performance parts, which are more fragile than the older, larger > geometries. > > -- Jim > > > _______________________________________ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
