Automatic Gearbox 4hp20 Citroen Xm

[CitroLover]

Hello guys,
I have a question about automatic gearbox from Citroën Xm V6 with ES9 engine. I bought it with broken gearbox, and instead of fixing its original gearbox I installed the gearbox from Citroën C5 V6.
And now can't change the gears. If I put it in Drive it shift, but stays in the first gear. After that it goes to Safe Mode (third gear)
So the car goes but there is no normal shifts between the gears. But it is the same gearbox 4hp20 from ZF. What could be the reason why doesn't work properly?
If anyone knows please share your experience!
Thanks

[xantia_v6]

The XM is very fussy about the source of a replacement gearbox.

The transmission ECU monitors the engine RPM and output RPM in each gear, and if the ratio doesn't match what it is expecting then it drops into limp mode.

The C5 and XM have different final drive ratios (and perhaps others).

I do have a spare (working) 4HP20 transmission from a 75000 mile XM, but it is located in France.

[CitroLover]

Xantia V6
Thank you very much for your reply.
Also one mechanic told me if I put gearbox ECU from Citroen C5 V6 it will fix the problem, in that case it will shift properly.
What would be the price of your gearbox? So it is original from Xm V6 ES9?

[xantia_v6]

A C5 ECU will likely not work because the C5 has multiplex wiring and the XM does not. I do know of someone who successfully fitted an ECU from a series 2 Xantia V6, but that was with a transmission from a Xantia.
Note also that petrol and diesel C5s have different ratios.
I am wanting £500 for the XM transmission, they are very difficult to find.

[CitroLover]

Well it is hm expensive.
What about the shipping cost? How much would be to send it to Bosnia and Herzegovina?