Have Mercedes Questions? Ask a Mechanic for Answers ASAP
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If a transmission service was not performed this may be a fault with debris in the transmission fluid causing improper operation of the valve body components in the transmission.I have seen this occur before.In this case a transmission flush/service will free up and remove debris from the transmission and correct this here.
The other issue is a fault with the valve body itself not operating properly.I have had to replace the valve body before for issues like this as well.Usually the check engine light will come on if this is a valve body fault or sensor or solenoid fault needing replaced so it may not need any repairs just a flush to free up and remove debris from the transmission and new fluid added then the transmission adaptations relearned.
The adaptations are relearned with a scan tool plugged into your vehicle that can communicate with the transmission computer and that can perform the adaptation reset.Normally this can cost around $300 or more in some cases to have the fluid changed and the adaptations reset.
This will have to be checked into further best done by a dealer or transmission repair facility that works on Mercedes vehicles to pinpoint and repair the fault here.
Let me know if you need anything else and feel free to rate my help.