What Are The Common Problems of The 722.6 Transmission?
Although the 722.6 transmission on the W210 can have mechanical problems (especially those on the pre-2000 models), the majority of the problems are actually small or electric, especially if the transmission has fewer than 150k mi.
If a transmission has major mechanical problem, then the only options are to rebuild the transmission or to install a used/new transmission. The typical mechanical problems are noise and/or metal in the oil pan or filter.
The pre-2000 model years tend to have more mechanical problems than the post-2000 models. This is primarily due to some upgrades in shaft bearing and valve body in the post-200 models.
To rebuild the transmission or install an already rebuilt transmission, the existing transmission has to be removed first. "nhmercracer" posted a procedure to remove the 722.6 transmission.
Rebuilding transmission is above the average DIYer and should be handled by special transmission shops or dealers so this FAQ stops the major mechanical problem discussion here.
The shifter bushing is a minor mechanical problem that is easy to fix. Again “G-AMG” posted this Photo DIY: Shifter Bushing Replacement
The three most common
problems that a DIY can repair are
1) Pressure Regulator Valve Spring
(This applies only to 1997, 1998, and 1999 models)
This spring affects the shifting from 2 <--> 3 and 3 <--> 4. If your transmission has rough shifting in these gears, then chances are this spring is either collapsed or completely broken. Here is a spring replacement DIY
2) Electrics Kit, aka, Conductor Plate or Electric Plate
(This affects all models)
722.6 Conductor Plate
The conductor plate is on top of the valve body and houses six solenoids and two sensors, a few other things. Common failures are the two speed sensors, which cannot be replaced separately so the entire conductor plate has to be replaced. This part has also received multiple updates so make sure you get the latest part.
When the speed sensors fail, the ETC does not know the input/output shaft speeds so it does not know what gear the transmission is in. If the failure is intermittent, then the ETC will go into “Mechanical-hydraulic” limp home mode. If the problem is more severe, then the ETC triggers the “electric” Limp Home mode.
Typical symptoms of speed sensor failure are erratic shifting or no shifting at all. The best diagnosis is to read the codes in the ETC using special scanners. If there are 012 (108) or 013 (109) codes, then the problems are likely the speed sensors.
If no special scanners are available, then at east read the codes using a generic OBD II scanner. Chances are the Check Engine Light (CEL) is on. If the codes are P0715 or P0720, again, the problems are likely due to the speed sensors. I said likely because the generic P0715 is mapped to several Mercedes codes. However, based on what has been seen, P0715 is a pretty reliable indicator of speed sensor failure.
Yours truly replaced the conductor plate
on a 1997 E320 and you can find the instructions here
3) Shift Module
(This affects all models, especially when you . . .
This is sometimes called the “liquefied module” problem.
Mercedes puts the cup holder near the shifter (for a reason) so you can spill your favorite drink into the shift module. Since the 722.6 is an electronic transmission and the shift module sits right below the shifter, unprotected and ready to receive your favorite drink, the favorite drink will cause the electronic parts in the module go crazy. The transmission could go into Limp Home mode and the CEL could turn on. If you check the codes, there could be some generic OBD II codes such as P0705, etc.
When this happens, you can try to take out the shift module and clean it thoroughly with electric contact cleaner and clear the codes in the ETC. If that does not work, you need a new shift module or a (working) used module.
Member “covinsky” detailed the procedure to remove the shift module
P.S. "G-AMG" posted a combined Photo DIY- 722.6 Conductor Plate and Regulator Valve Spring R/R