Hi,
I am not really sure if your truck model is serial E387 or E1276.
Error code T326 means "Safety relay contact is closed although relay is not activated"
The Safety relay is located inside the controller LDC A2, open the cover of the LDC you can see it locating at the corner of the PCB which looks likely a small rectangle box around 30 mm square with the copper-yellow color.
In this case, the contact tips maybe sticky, find the way to clean it or replace the one.
Good luck