simon,
here are some possible causes for this error
- wire break in T1 or T2 IGBT
- faulty wire connection
- faulty drive board
- faulty traction current sensor CS1
- faulty traction logic card

now they do go on to say to disconnect the battery and check the armature wiring for breakage and shorting. Then check the IGBT circuits and drive board for anything abnormal. Then check the current sensor and finally if no other issues found to replace the logic board.

when you check the drive board pay attention to the diodes, they are known to burn generally because of running the truck at low battery voltages causing a high amp draw across those diodes.

good luck