i believe FH means Battery Voltage out of range
Wrong voltage battery or voltage out of range.
Says to run test A-15

Battery sense voltage at JPT24-24 must read within a range of:
24v truck = 22.0 to 26 volts
36v truck = 33.0 to 39 volts

diagnostic says to test at
step 1: TP1 (+ lead) to TP4 (ground) if pass go to next step, if fail check batt voltage/SG
step 2: JPF4-1 (+ lead) to TP4 (ground) if pass go to next step, if fail check harness TP1 to TP4.
step 3: JPF4-7 (+ lead) to TP4 (ground) if pass go to next step, if fail replace fuse relay card
step 4: JPT24-24 (+ lead) to TP4 (ground) if pass replace VCM, if fail check harness from fuse relay card to VM.
expected voltage on all tests are:
24v truck = 16 to 32v
36v truck = 28 to 44v