-99 means that the service reminder interval has been tripped. With a GE Handset, set Functions 19 and 20 both to a value of 255 if you want to eliminate the service reminder. Then -99 will not appear again. On the reach truck, -01 will appear when brake "deadman" pedal is up.
-01 on the ECG, Park Brake switch open. Or Seat Switch open (if equipped), Slide in Battery retainer interlock switch open (if equipped).