I am pretty sure you can also get a code 51 if you have not properly setup the controller, too.

Code 51>Capacitor volts are too low before line contactor closes.
1. PTC defective
2. An accessory or component other than the motor controllers
is connected to load side of line contactor.
3. Repeated charging/discharging the capacitors during
troubleshooting may cause a Status Code 51. If the PTC
is hot, allow it to cool.
4. Status code will occur if the line contactor does not
close properly and truck operation is attempted.
5. Status code will occur if battery voltage drops below
50% nominal voltage.