Check fluid level. You need the factory tool dipstick.

Check the electrical connector on the US passenger side of the transmission. There’s probably an aluminum shield that takes a T30 driver. Then flip the bayonet tab down to release the plug. It’ll probably be wet with ATF. The socket has a center bolt that takes a 7mm socket. Loosen the bolt, it’s captive, to remove and replace the socket. It’s called a pilot bushing in the EPC. $15-20 for MB brand item.

Check the TCM for ATF contamination. Fluid seeps up the harness and pools in the TCM case. Open the box on the US passenger side of the engine bay. Look for the skinniest module, likely second from the front. Unplug it then turn it upside-down to see if fluid pours out. It might take up to a hour upside-down for fluid to leak out. If there’s fluid, carefully pry the board from the case. Clean it with electronic parts cleaner.

I don’t know if there are TCM codes to clear without a CEL (you didn’t say if the CEL is illuminated). If you have access to SDS, check for codes, note them, then clear the codes.

If that doesn’t do it, you might need a conductor plate (manageable DIY), or something more involved.

Sixto
98 E320s sedan and wagon
02 C3/0 wagon