Hi friend,

I assume that you know what the error 104 mean. But just think that:
Possible causes:
1. Cable connections between seat switch (S4)and controller (N1:33, N1:38) faulty.
2. Cable connections between pedal position sensor (1B2) and controller (N1:1, N1:32, N1:49, N1:61) faulty.
3. Seat switch (S4) defective.
4. Pedal position sensor (1B2) defective

These 2 signals are not synchronized each other may cause to stop the Engine to start. please check and try to clear this error before doing the next step.

Furthermore, This truck has 2 speed sensors : Engine speed sensor and truck speed sensor. So you need to check the other one as well. This is because the controller normally couldn't know if the speed sensor is in good or not so he never alarm an error for speed sensor problem.
Good luck
Nuna