A manufacturing plant reported that a Crown FC 5200 4,000-lb capacity electric counterbalance forklift had developed a progressive travel fault over a three-week period. The truck would operate normally for the first portion of a shift, then intermittently become unresponsive to travel-pedal input - the operator pressing the accelerator and the truck failing to respond for one to three seconds before the travel function returned. The events became progressively more frequent as shifts progressed, and by the end of an 8-hour shift the truck would sometimes lose travel power entirely for 5-to-10-second intervals, requiring the operator to release the pedal and re-apply before travel resumed. The cab display intermittently showed a "Travel System" fault code during the unresponsive events.
The technician first verified the battery's state of charge and condition - the battery was fully charged and showed no significant cell-imbalance issues on the diagnostic tool. He then connected the Crown Access 1 2 3 diagnostic tool and retrieved the stored fault history. The log showed repeated "Travel Pedal Signal Fault" and "Traction Controller Input Timeout" codes across the past 140 operating hours, with a clear pattern of increasing frequency as operating hours accumulated.
He understood the FC 5200's travel-control architecture. The truck's travel system uses a "Travel Potentiometer" mounted beneath the accelerator pedal - a variable-resistance sensor whose wiper moves across a resistive track as the operator presses the pedal, converting pedal position into an electrical signal sent to the "Traction Controller." The controller reads the potentiometer's signal and commands the traction motor's power switches accordingly. When the potentiometer's wiper track wears, becomes contaminated, or develops intermittent contact, the signal to the controller drops out or becomes erratic - producing the dead-pedal events the operator described. When the traction controller's internal capacitors degrade, the controller's signal processing becomes unstable under load, compounding the intermittent behavior.
He retrieved live data during a loaded travel test and observed the travel potentiometer's signal output. During normal operation, the signal tracked smoothly from 0.4 volts at rest to 4.6 volts at full pedal depression. During the fault events, the signal would intermittently drop to zero or spike erratically - even with the pedal held at a constant position - confirming the potentiometer's wiper was losing contact with the resistive track intermittently under load.
He removed the travel potentiometer and disassembled it. The potentiometer's internal wiper track showed visible wear - the resistive track's surface had worn thin in the region corresponding to the pedal's most-used travel range, and fine carbon debris had accumulated within the track's contact zone. The wiper's contact arm showed corresponding wear at its tip. He further inspected the traction controller's internal components after removing its cover. The controller's input-stage capacitors showed visible swelling at their tops - a classic indication of electrolyte loss and degraded capacitance - and two capacitors showed small electrolyte leaks at their bases. The degraded capacitors had compromised the controller's signal processing, compounding the intermittent behavior introduced by the worn potentiometer.
The root cause was traced to travel potentiometer wear compounded by traction controller capacitor degradation. The potentiometer's wiper track had worn naturally over extended service (the truck had approximately 6,800 hours of warehouse duty), and the resulting intermittent signal loss had produced the dead-pedal events. The controller's degraded input-stage capacitors had compounded the fault by destabilizing the controller's signal processing under load, extending the duration of the unresponsive events.
The repair involved replacing the travel potentiometer with a new unit, replacing the traction controller's input-stage capacitors with new components rated for the controller's operating temperature, and cleaning the controller's internal board with contact cleaner to remove any electrolyte residue. The controller's cooling duct was cleaned to restore airflow across the heatsink, and all electrical connections were verified torqued to specification. The travel controller's calibration was verified and reset using the Access 1 2 3 diagnostic tool. After reassembly, a full-shift loaded operational test showed no dead-pedal events, no travel power loss, and the "Travel System" fault code did not recur. Travel potentiometer inspection and controller capacitor condition checks were added to the truck's annual inspection checklist.
