When the cost of replacement components stacks up on Toyota drive systems I replace the complete system with a Curtis control unit, cheaper and less fault finding in the future.


Having said that, CO is mostly commonly caused by damaged power transistors (typically caused by using the forklift to push something). As already mentioned change all the drive power transistors as they are matched otherwise you will get thermal runaway and damage the transistors again AND ALWAYS change the flywheel diodes, they protect the transistors from back emf caused when the transistors switch the inductive load, ie the motor. On the FBMF models I have found diodes also short circuited on the drive control boards.

If the main CPU board is damaged along with the power transistors I call a halt and retrofit with a Curtis control unit. I use the MG, regen contactor, to drive the hydraulic motor and the pump contactor as a line contactor for the Curtis controller. This saves buying a contact assembly for the line contactor and saves having to find space to accommodate it plus reduces the amount of wiring required to connect the Curtis unit.
On one occasion I found the line contactor overheated every 6 months which was due to a poor battery so to save on replacing the battery I added a cooling fan next to the line contactor.