Hello,
This will probably not be a TruckersMP problem, but a configuration or hardware problem. You can try to redefine the settings as suggested, in addition, check that the steering wheels you use are working correctly, that they are properly calibrated and adjusted to be used in the game.
There is also an existing configuration in the game depending on how that wheel is used (instead of 'steering wheel' use 'joystick' in the configuration options of controls within the game).
The game obeys commands sent by hardware devices, if those devices do not work correctly the commands sent to the game will not be accurate or may not work.
Please keep us informed about your problem, if possible, you can tell us which steering wheel you are using to make it easier for us to assist you.
From now on, peace and good.