The 722.6 has been a very reliable electronic transmission and is much more simple to repair than its predecessors. One problem that was ongoing with this transmission are leaks at the plug adapter for harness connector. There are various versions of this adapter and o-rings, some have tabs, the adapter is best replaced complete with o-rings. If the adapter o-rings should be black, red or white o-rings are prone to leak, connectors with tabs will also leak. The electronic transmissions are lifetime fill in most cases and have a lock on the dipstick. If you replace the adapter you need to adjust the fluid level, the transmission dipstick is a special tool. The fluid used is not Dexron III but a variant of it, don’t use ordinary A/T fluid in an electronic transmission with lifetime fill. The correct fluid is 001 989 21 03, MB 236.10. This fluid is backward compatible with all earlier transmissions. The dipstick is a special tool and the dipstick cap has an anti-tamper plastic lock. The fluid after MY 2006 is the same in a 722.6 as a 722.9, don’t use the 722.6 fluid in a 2006. The newer fluid is slightly purple in color. The newest fluid is backward compatible with all Mercedes transmissions. Some late model 722.6 transmissions have a scheduled transmission service, oil and filter, at 39k. For all others even if its not required a transmission service if done with the correct fluid could only be beneficial, even if it isn't called for.
Early 722.6 transmissions had a poor valve body conductor plate design, this part has the starter lock out switch and transmission VSS sensors built into it and powers the shift solenoids. If it fails you may have an intermittent no-crank no-start condition and the transmission may shift irregularly because the speed sensor signals needed for calculate smooth shift adaptations are faulty. This part can be replaced with the transmission in the vehicle and the valve body removed, this is good to do if considering a transmission service on an older vehicle. If you are experiencing shifting concerns or start delay, please contact us for details as we can scan for codes that would indicate you need this repair or other transmission repairs.
One note on torque converters and transmissions, there is considerable variation in these parts and the best repair is installing and Mercedes-Benz remanufactured unit as it will be an exact match. Used parts will in most cases not match and may be problematic even if they are good, control units can be very specific and may not work correctly. Dealer remanufactured is the highest cost option but is the best and fastest turn around. Alternately, we can rebuild your transmission, and have your existing torque converter rebuilt depending on the extent of the damage. A torque converter may be rebuilt. They are sent out for this repair. They are punch marked, cut in half by a dedicated machine and cleaned of any debris. Inspected and the lockup clutches replaced if needed and welded back together on a dedicated machine. We don't recommend replacing one with an aftermarket remanufactured one, you are best to have the one from the vehicle rebuilt. There are too many variations of these to expect you will get the correct one, although it will fit, internally it will have a different design and stall characteristics. A new unit from Mercedes is the best repair but it may be over 3x the price of having yours rebuilt. In many cases the torque converter is replaced simply because it may be contaminated with material from the failed transmission and if it is reused the new transmission may be damaged, having it opened inspected and rebuilt eliminates this concern.
Another issue with the 722.6 involves transmission fluid wicking up the harness into the control module and causing the module to malfunction. Usually, the harness from the transmission to the ETC module is replaced and the module is replaced provided the leak is repaired. In some cases this may be more than is actually needed but it usually fixes the concern. Transmission fluid does not actually damage the module and can be flushed away with board cleaning solvent or electrical contact cleaner as a first attempt. Always repair the leak before replacing a module.
Another issue with the 722.6 was in Valeo radiators leaking coolant into the transmission fluid, this causes and harsh engagement followed by a droning vibration. There is a glycol test to determine if this is the case. If strongly positive the radiator, torque converter are replaced and the transmission and lines flushed. The dealer used to replace the transmission also but no longer does this commonly. If the contamination is slight the radiator only is replaced and the lines and transmission flushed. Consider having the transmission clutches replaced if the contamination is high, i.e. visible contamination. The clutches are very sensitive and it may not be fully repaired unless the radiator, torque converter and transmission are replaced or rebuilt. If you have this complaint and the glycol contamination is not present you may need a new transmission control unit, the newest software can correct an adaptation issue with the torque converter than can also be the cause. This should be diagnosed by a specialist. The transmission control unit is replaced and adapted to repair this because the transmission software is not flash updatable as it is on the predecessor.
Early 722.6 transmissions had a poor valve body conductor plate design, this part has the starter lock out switch and transmission VSS sensors built into it and powers the shift solenoids. If it fails you may have an intermittent no-crank no-start condition and the transmission may shift irregularly because the speed sensor signals needed for calculate smooth shift adaptations are faulty. This part can be replaced with the transmission in the vehicle and the valve body removed, this is good to do if considering a transmission service on an older vehicle. If you are experiencing shifting concerns or start delay, please contact us for details as we can scan for codes that would indicate you need this repair or other transmission repairs.
One note on torque converters and transmissions, there is considerable variation in these parts and the best repair is installing and Mercedes-Benz remanufactured unit as it will be an exact match. Used parts will in most cases not match and may be problematic even if they are good, control units can be very specific and may not work correctly. Dealer remanufactured is the highest cost option but is the best and fastest turn around. Alternately, we can rebuild your transmission, and have your existing torque converter rebuilt depending on the extent of the damage. A torque converter may be rebuilt. They are sent out for this repair. They are punch marked, cut in half by a dedicated machine and cleaned of any debris. Inspected and the lockup clutches replaced if needed and welded back together on a dedicated machine. We don't recommend replacing one with an aftermarket remanufactured one, you are best to have the one from the vehicle rebuilt. There are too many variations of these to expect you will get the correct one, although it will fit, internally it will have a different design and stall characteristics. A new unit from Mercedes is the best repair but it may be over 3x the price of having yours rebuilt. In many cases the torque converter is replaced simply because it may be contaminated with material from the failed transmission and if it is reused the new transmission may be damaged, having it opened inspected and rebuilt eliminates this concern.
Another issue with the 722.6 involves transmission fluid wicking up the harness into the control module and causing the module to malfunction. Usually, the harness from the transmission to the ETC module is replaced and the module is replaced provided the leak is repaired. In some cases this may be more than is actually needed but it usually fixes the concern. Transmission fluid does not actually damage the module and can be flushed away with board cleaning solvent or electrical contact cleaner as a first attempt. Always repair the leak before replacing a module.
Another issue with the 722.6 was in Valeo radiators leaking coolant into the transmission fluid, this causes and harsh engagement followed by a droning vibration. There is a glycol test to determine if this is the case. If strongly positive the radiator, torque converter are replaced and the transmission and lines flushed. The dealer used to replace the transmission also but no longer does this commonly. If the contamination is slight the radiator only is replaced and the lines and transmission flushed. Consider having the transmission clutches replaced if the contamination is high, i.e. visible contamination. The clutches are very sensitive and it may not be fully repaired unless the radiator, torque converter and transmission are replaced or rebuilt. If you have this complaint and the glycol contamination is not present you may need a new transmission control unit, the newest software can correct an adaptation issue with the torque converter than can also be the cause. This should be diagnosed by a specialist. The transmission control unit is replaced and adapted to repair this because the transmission software is not flash updatable as it is on the predecessor.
