'Fr' , 'FL', and F apply to the failure protection circuit and will be displayed if a condition exists that could cause the operator to loose control of the lift truck speed. a short circuit in the drives can cause the logics to deactivate the line contactor and the line contactor is commanded to open to prevent any further issues.

FL does indicate a problem in the left side and is detecting a high voltage on wire 41 emitter.

this is what the troubleshooting chart says for this code:
check the left power transistor circuit
with battery disconnected remove logics cover and check continuity of wire 41 at emmiter of 1TRNL to P2-10 on logic.
if no continuity repair wiring, if continuity replace logics.

i would still look closely at the transistor, it may be bad and causing this code.