Hi. Skyreach,
Is the issue when you put the truck in sideways mode, the rear wheel starts to change to 90 but the front wheel do not.
If so, First thing to check is that the rear proxy is seeing the rear wheel turn to the 90. Check the stopper bolt is not limiting it, check that the rear proxy has read the plate (spacing around 8mm). If the rear proxy is reading the rear wheel turned to 90, then this signal is used to switch the change over valve, opening a solenoid that then allows the oil to the front right master cylinder which in turn also moves the left slave cylinder. This continues until the front left wheel 90 proxy reads the front plate and stops the sequence.

Hope this helps,