Here is a full list of the early codes for you:
00010 EEPROM not programmed
00013 Converter clutch solenoid valve - circuit interrupted
00014 Pressure regulator solenoid valve - circuit interrupted
00015 1-2/3-4 shift - circuit interrupted solenoid valve
00016 2-3 shift solenoid valve - circuit interrupted
00017 1-2/3-4 shift - short circuit to ground solenoid valve
00018 2-3 shift solenoid valve - short circuit to ground
00025 1-2/3-4 shift - short circuit to battery solenoid valve
00028 2-3 shift solenoid valve - short circuit to battery voltage
00029 Converter clutch solenoid valve - short circuit to ground
00031 Transmission output speed signal - Not present, short to ground or no voltage
00032 Pressure regulator solenoid valve - short circuit to ground
00033 Pressure regulator solenoid valve - short circuit to battery voltage
00034 Brake band solenoid valve - short circuit to battery voltage
00035 Brake band solenoid valve - short circuit to ground
00036 Converter clutch solenoid vale - short circuit to battery voltage
00039 Transmission output speed - incorrect signal (vehicle speed = 0)
00041 Transmission fault - Vehicle speed is to high relative to actual gear
00044 Braje band solenoid valve - circuit interrupted
00045 Permanent voltage - circuit interrupted
00048 Battery voltage low - (less tahn 9V)
00049 Battery voltage high - (greater than 16V)
00051 Control unit fail - EPROM defective
00055 Control unit fail - EPROM check sum fault
00056 Selector lever position switch - Function, adjustment
00057 Load signal from diesel electronics - Position of accelerator pedal (cruise control)
00058 ETR signal - (Engine Torque Reduction stage)
00059 Park/neutral output to control unit - Short circuit to ground
00060 Supply solenoid valves - circuit interrupted
00061 Monitor relay, current supply for - Short circuit to battery voltage solenoid valves in TCM
00062 Monitor relay, current supply for - Short circuit to ground voltage solenoid valves in TCM
00063 Monitor relay, current supply for - Circuit interrupted solenoid valves in TCM
00064 Monitor relay, current supply for - Watch dog defective solenoid valves in TCM
00065 Transmission fluid temperature sensor - short circuit to bat voltage
00066 Transmission fluid temperature sensor voltage low - short circuit to ground
00068 Transmission fluid temperature sensor - Temperature above 130degC
00069 Information output via P/N - Short circuit to battery voltage
00071 TV load signal - circuit interrupted or short circuit to battery voltage
00072 Fault in diesel injection
00073 Fault of diesel engine temperature sensor
00074 Load signal - short circuit to ground
00075 Torque control circuit - short circuit to battery voltage
00076 Load signal - short circuit to battery voltage
00077 Kickdown circuit - short circuit to ground
00078 Shift period to long
00079 Kickdown switch - circuit interrupted
00081 ETR signal (Engine Torque Reduction) - circuit interrupted or short to battery
00082 Selector lever position switch incorrectly - remain in last valid display and then adjust enter D mode
00083 Torque control - short circuit to ground
00084 Brake switch - remains closed
00085 Control unit fail - fault in torque control
00086 ETR (Engine Torque Reduction) - Signal frequency outside specified range)
00089 ETR signal - Control unit fault (TC not activated)
00091 MIWG signal, transmission torque increase - short circuit to battery voltage
00092 MIWG signal, transmission torque increase - circuit interrupted or short circuit to ground
00095 Winter program display
00096 Winter program display
00097 Output display
00098 Output display
00111 Barometer
00112 Barometer
So, 56 indicates a fault with the selector switch position.....so its worth checking the adjustment