I purchased the 2002 C320 with it being stuck in 3rd gear. Scanned with foxwell NT510Elite and P2502, P2069 both from N15/3 ETC EGS control unit, and generic code P7030.
I replaced the 13 pin connector and conductor plate. Fluid was new as the previous owner had just did the same thing as the plate and 13 pin conn were new and he changed the ETC or TCU as the TCU had c240 written on the back of it like a salvage yard would do. No change still stuck in 3rd same codes. Replaced the TCU with used one from 2003 C320 cleared codes and was able to shift into 4th and 5th if i manually shifted. If I let it shift automatically it stuck in 3rd and wont allow me to manual shift unless I turn key off and back on. I tried to reprogram or reset TCU with Foxwell scanner but it locks up upon starting the adaption. Getting ready to just replace the tranny with one I got from a 2003 C230 had no issues at all. Would hate to do that if I dont absolutely have to. Thanks for any info suggestions ideas or any help.

Look for ATF contamination in the connector where you plug in the TCU. ATF can migrate into the plug and insulate the pins. That's what caused my trans to get stuck in limp home mode (2nd gear). ATF can wick up the tape wrapped around the wiring harness. If that all checks out you could have a bad solenoid or valve body. You can get a JY valve body and solenoids for dirt cheap. I wouldn't replace the entire trans unless there was obvious evidence of damage like chunks of metal or clutch material in the filter or coolant contamination. Early 203s had valeo radiators that sometimes let ATF and coolant mix.

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Thanks tjts1 for your response,

Yeah I was a bit worried about having that radiator and it may have had it.
The previous owner changed fluid and conductor plate filter and pan gasket.
When I got it all was very clean but I have no way of knowing what it looked like when he opened it. could have been trashed and he didnt want to deal with it. also I did change the valve body and sillynoids. My post was getting

pretty lengthy though. That is when i was able to get past 3rd gear and into 4th but it was a harsh shift and threw the implausable gear code. I can however manually shift now without throwing any codes, kind of crazy...I just read about a spring in the vb that breaks or gets weak and stops 4th gear shift. Could that be a possibility? Thanks again for your time.
Don

Yes there are a number of springs, and tiny little steel balls in the valve body that can cause problems if they're broken or messed with. I did a valve body rebuilt once. It's doable but not fun. If I had to do it again I would take my chances with a JY valve body.
https://imgur.com/a/8X4RT75
https://youtu.be/LdF5DnGwz7E
On my other car (E320) I ended up replacing the torque converter lock up solenoid to cure harsh shifts. My foxwell nt520 has a diagnostic mode hidden in one of the menus that lets you shut off the torque converter lock up solenoid. When I did that, super smooth shifts. TQ solenoid is most likely to fail because it's used in every gear. I suspect nt510 can also do that.

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