Material Handling Equipment Troubleshooting Q&A

Material Handling Equipment Troubleshooting — real-world interview & field troubleshooting questions with clear, practical answers. Tap any question to open its answer.

Showing the first 70 questions free. The complete question bank is available as a PDF below.

ELECTRIC FORKLIFTS & REACH TRUCKS (TRACTION, STEER & MAST HYDRAULICS)

Q1An electric counterbalance forklift lifts rated loads normally, but moves at barely 2 km/h in turtle creep speed. What input interlock failed?

AnswerSeat presence safety switch open circuit, handbrake microswitch stuck engaged, or mast height limit switch stuck active (locking drive into slow travel speed while forks are elevated).

Q2A 48V electric reach truck hydraulic lift pump groans loudly and mast lifting shudders violently. Where is the hydraulic fault?

AnswerAir ingestion into the hydraulic lift pump suction line, low hydraulic oil level in the tank, or a clogged suction oil strainer causing pump cavitation during high-displacement lift cylinder demand.

Q3How do you test whether an electric forklift MOSFET traction controller has a blown short-circuit power arm?

AnswerDisconnect the 48V traction battery. Discharge internal capacitor banks. Measure diode drops across the B+ to Motor Phase terminals (U, V, W) and B- to Motor Phase terminals with a multimeter on Diode Mode. A 0.0V reading confirms shorted MOSFET silicon.

Q4An electric forklift steering wheel spins continuously with zero resistance, but the rear steer wheels do not turn. Cause?

AnswerSteer-by-wire rotary encoder coupling sheared on the steering column, electronic steer motor controller fuse blown, or hydraulic orbitrol steering unit cross-port relief valve stuck wide open.

Q5When lowering a 2-ton pallet, the mast stops descending abruptly 300 mm above the floor and locks up. What safety valve triggered?

AnswerHydraulic velocity fuse (hose rupture safety valve) tripped. Mounted in the base of the lift cylinder, excessive lowering speed creates dynamic pressure drop that snaps the internal poppet shut to prevent a free-fall crash.

Q6An electric forklift's regenerative braking fails to slow the truck when the operator releases the accelerator on a downhill ramp, and the truck coasts freely instead. What should be checked?

AnswerRegenerative braking disabled in the traction controller parameters, or a faulty accelerator potentiometer failing to signal a clean release-to-zero condition. Verify controller regen parameters are enabled and correctly scaled, and check pedal sensor output returns cleanly to 0% throttle.

Q7A reach truck's mast free-lift stage rises normally but the second and third stages fail to extend under load. What hydraulic cause is most likely?

AnswerInsufficient pressure reaching the secondary lift cylinders from a sticking sequence/priority valve, a worn lift pump unable to build full pressure under load, or a partially blocked flow divider. Check system relief pressure against spec and inspect the sequence valve for sticking.

Q8An electric forklift's traction motor makes a high-pitched whine only when accelerating from a stop, but is silent at steady speed. What is the likely cause?

AnswerNormal PWM switching audible under high current demand during acceleration, or bearing wear generating a load-dependent whine. Compare against a known-good truck of the same model; if unusually loud, inspect the traction motor bearings.

Q9A forklift's battery discharge indicator shows a normal reading, but the truck loses power abruptly mid-shift as if the battery were empty. What should be investigated?

AnswerA loose or corroded main battery connector causing high resistance under load, or a battery cell going open-circuit under high current draw even though its resting voltage reads normal. Inspect the connector contacts and load-test individual cells for one that drops out under load.

Q10An electric forklift intermittently loses all electrical power for a split second while driving over an uneven section of floor, then resumes normally. What should be checked first?

AnswerA loose or vibration-damaged main power connector or key-switch harness momentarily opening circuit under mechanical shock. Inspect and secure all main power connections and harness routing for chafing or looseness near the impact point.

OVERHEAD CRANES, WIRE ROPE HOISTS & GANTRY SYSTEMS

Q11An overhead crane wire rope exhibits 'bird-caging' and broken outer strand wires near the hook block. Immediate mandatory action?

AnswerREMOVE FROM SERVICE IMMEDIATELY. Bird-caging (loosening and ballooning of outer strands away from core) indicates severe shock loading or torsional unbalance. ASME B30.2 strictly mandates immediate disposal; never attempt to straighten or load-test.

Q12An overhead crane travels forward with a severe diagonal skew, causing wheel flanges to screech and grind against the runway rail. Why?

AnswerWheel diameter mismatch on dual drive wheels (one wheel worn smaller), non-synchronized dual VFD drives, or rail span dimension out of tolerance ($S > \pm 5ext{ mm}$). The crane crabs diagonally until wheel flanges bind on rail heads.

Q13A wire rope hoist electro-magnetic disc brake slips, allowing suspended 5-ton loads to drift downward 200 mm after releasing the pendant. Fix?

AnswerBrake air-gap adjustment. Worn friction pads have widened the armature air gap beyond limit (>0.8 mm), weakening magnetic pull and spring clamping pressure. Adjust brake air gap using feeler gauges to factory spec (typically 0.3–0.4 mm).

Q14What causes an overhead crane hoist wire rope to cross grooves and wrap over itself on the grooved rope drum?

AnswerFleet angle exceeding 1.5 to 2.0 degrees, a broken or missing mechanical rope guide ring, or hoisting with the load swinging violently diagonally off-center from the vertical hook axis.

Q15Why do crane hoist motors strictly require an independent, geared upper rotary limit switch in addition to a paddle limit switch?

AnswerRedundancy against two-blocking catastrophic failure. Two-blocking occurs when the heavy hook block collides directly into the rotating drum, snapping wire ropes and dropping the load. The paddle switch is primary; the rotary gear switch is secondary fail-safe.

Q16An overhead crane's hoist motor trips on overload only when lifting loads near rated capacity, even though the load is within the certified limit. What should be checked?

AnswerAn overly conservative thermal overload setting, a worn hoist gearbox increasing mechanical drag, or the brake not fully releasing and adding drag during lift. Verify the overload setting against the motor nameplate, check gearbox oil condition, and confirm full brake release.

Q17A gantry crane's end trucks show uneven wheel wear, with one side wearing significantly faster than the other. What alignment issue is indicated?

AnswerRunway rail misalignment or unequal span between rails, or unsynchronized drive wheel speeds causing the crane to crab and load one side's flanges more. Survey rail alignment/span against tolerance and verify both drive motors/VFDs are synchronized.

Q18A wire rope hoist's upper limit switch fails to stop the hook block, allowing it to nearly two-block into the hoist drum before the operator releases the control. What should be inspected?

AnswerA failed or maladjusted upper limit switch (lever not tripping, or contacts welded closed), or a bypassed limit switch left disabled from a prior maintenance action. Test limit switch operation immediately, replace if faulty, and never operate with safety limits bypassed.

Q19An overhead crane's bridge travel is smooth in one direction but jerky and hesitant in the opposite direction. What should be investigated?

AnswerDirectional contactor contacts pitted or partially failed on the hesitant direction, or unequal brake release timing between the two bridge drive motors. Inspect and clean/replace the affected contactor, and verify both bridge brakes release simultaneously.

Q20A crane's overload protection system indicates a load weight consistently about 10% higher than the load's actual known weight. What should be checked?

AnswerLoad cell calibration drift, or unaccounted tare weight from an attached lifting fixture not zeroed out of the system. Recalibrate the load cell against a certified test weight, and confirm the system tare is correctly set with the actual rigging in place.

AGVS, AMRS, ASRS & AUTOMATED SHUTTLE SYSTEMS

Q21An Autonomous Mobile Robot (AMR) using LiDAR SLAM stops in open corridors, spinning in circles searching for position ('lost robot'). Why?

AnswerFeatureless environment or dynamic map corruption. Wide open, featureless glass/plain corridors provide insufficient static reflection corners for 2D LiDAR matching, or warehouse layout changes (moved pallets) diverged >40% from stored master point cloud.

Q22An AGV tracking a magnetic floor tape loses the line at every sharp 90-degree corner, drifting into manual fault stop. Root cause?

AnswerVehicle cornering speed too high, magnetic sensor array mounted too high off the floor (>25 mm gap weakens magnetic flux below detection threshold), or damaged/demagnetized floor tape at turn radiuses.

Q23A safety laser scanner on an AMR trips into protective stop even when no humans or obstacles are within 3 meters. Remedy?

AnswerAirborne dust, water steam, or highly reflective safety vests / metal doorframes blinding the time-of-flight (ToF) laser receiver. Clean scanner optical window with microfiber cloth and configure dirt-suppression filter in scanner software.

Q24An AMR differential-drive wheel slips and spins freely, failing to dock into pallet charging stations accurately. Fix?

AnswerLoss of spring suspension downforce on drive wheels. Unlike caster wheels, spring-loaded drive wheels must maintain constant floor contact force. Worn suspension springs or polyurethane tire tread peeling breaks friction.

Q25An AGV fleet management server drops Wi-Fi communication with Vehicle #4 every time it passes near robotic welding cells. Why?

AnswerIntense RF/electromagnetic interference (EMI) from high-frequency TIG/MIG arc ignition blinding 2.4 GHz Wi-Fi transceivers, or weak Wi-Fi access point handoff roaming thresholds. Switch AGV network to 5 GHz with 802.11r fast roaming.

Q26An ASRS crane telescopic extraction fork extends into a rack, drops a pallet, and alarms on 'Fork Torque Limit Exceeded'. What failed?

AnswerThe rack beam deflected downward under load, leaving insufficient vertical clearance for fork withdrawal, or the telescopic rack-and-pinion fork slide chain stretched and skipped a tooth.

Q27An ASRS stacker crane traveling at 4 m/s overshoots its target rack bin by 150 mm, triggering emergency buffer collision. Why?

AnswerLaser distance meter (optical ToF sensor) optical window dirty, barcode positioning strip damaged/peeling along the floor rail, or drive motor regenerative brake chopper resistor failed.

Q28An autonomous pallet shuttle inside a deep-lane racking system stops responding and displays battery flat in the middle of a 30-meter tunnel. Recovery?

AnswerUse a specialized manual recovery tether hook or dispatch an auxiliary rescue shuttle equipped with an electromagnetic coupling latch to physically drag the dead shuttle out to the retrieval aisle.

Q29A stacker crane vertical hoist rope slack-switch trips randomly during high-speed downward moves with an empty carriage. Cause?

AnswerEmpty carriage vertical deceleration rate ($a$) exceeded gravitational acceleration ($a > g$). The carriage momentarily weightless floated off the ropes. Reprogram hoist servo deceleration ramp curve in the PLC.

Q30What diagnostic check resolves intermittent optical communication drops on an ASRS infrared optical data transceiver?

AnswerCheck transceiver line-of-sight optical alignment using visible laser pointer tool, clean front optical lens covers with antistatic fluid, and ensure building structural expansion joints are not shifting crane rails.

ORDER PICKERS, PALLET JACKS & SCISSOR LIFTS

Q31An electric pedestrian pallet jack brake will not release: the tiller arm is pulled down, but the drive wheel stays locked. What failed?

AnswerTiller arm base hall-effect angle sensor dead-band fault, severed wiring in the folding tiller hinge harness, or the 24VDC electromagnetic brake coil open-circuited.

Q32A mobile hydraulic scissor lift rises to 6 meters, but creeps slowly downward by 100 mm every 5 minutes with no controls touched. Diagnosis?

AnswerInternal leakage in the hydraulic cylinder piston seals, or the manual emergency descent needle valve / lowering solenoid valve seat is scored and leaking fluid back to tank.

Q33The belly-button emergency reverse safety button on an electric walkie pallet truck does not function when tested. Immediate risk?

AnswerEXTREME CRUSH HAZARD. The belly button reverses drive motor direction if the operator is pinned against a wall. A broken microswitch or jammed actuator spring means the machine will crush the operator. Lock out truck immediately.

Q34An order picker platform drive is inhibited whenever the mast elevates above 3 meters height. What safety system is active?

AnswerSlack chain / height interlock safety. Driving at full speed with elevated mast causes rollover. When the height sensor asserts >3 m, vehicle speed is clamped to crawl speed (<1.5 km/h) and steer angle is electronically limited.

Q35A hydraulic scissor lift tilts diagonally and binds while elevating, straining the scissor arm bushings. Cause?

AnswerUneven wear or seizure of scissor arm slide block guide shoes, dry pivot pin bushings lacking grease, or asymmetric dual-cylinder hydraulic flow distribution.

Q36An electric pallet jack's forks lift normally when empty but stall partway up under a loaded pallet. What should be checked?

AnswerA hydraulic pump motor unable to sustain pressure under load due to worn brushes or a weak battery sagging under current draw, or a relief valve set too low bypassing oil before full pressure. Check battery voltage under load, inspect pump motor brushes, and verify relief valve setting.

Q37An order picker's platform drifts downward slowly on its own while the operator is stationary at height, without any control input. What should be inspected?

AnswerInternal leakage past the lift cylinder piston seal, or a lift-hold valve not seating fully, allowing oil to bypass back to tank over time. Test cylinder drift rate against the manufacturer's allowable limit, and replace worn cylinder seals or the hold valve if leakage exceeds spec.

Q38A scissor lift's platform tilts to one side when raised, even though both hydraulic cylinders appear to extend at the same rate. What should be checked?

AnswerUneven flow between the two lift cylinders from a partially restricted hose/fitting on one side, or unequal cylinder wear. Check for a synchronizing valve if equipped, inspect for restrictions, and verify both cylinders are mechanically identical.

Q39An order picker's drive wheel loses traction and spins on a wet or oily section of floor, triggering an unexpected stop. What safety system responded, and what should be checked?

AnswerWheel-slip/anti-rollback traction control detecting a speed mismatch between commanded and actual wheel speed and cutting drive power as a safety response. Clean the affected floor area, inspect drive tire wear, and verify traction control sensitivity is set appropriately for the environment.

Q40A pallet jack's steering becomes very heavy and difficult to turn, especially when loaded. What mechanical cause is most likely?

AnswerWorn or dry steering column bearings/bushings, a bent steering shaft from impact, or excessively tight castor wheel bearings creating drag. Lubricate steering bearings per schedule, inspect the steering shaft for straightness, and check castor wheels rotate freely.

TOW TRACTORS, TUGGERS & PNEUMATIC TUBE TRANSPORT

Q41An industrial warehouse tow tractor pulling 4 heavy cart trailers fails to stop within safe distance, locking drive wheels and jackknifing. Cause?

AnswerOperating without trailer overrun brakes / inertia brakes on towed carts. The unbraked kinetic momentum of 4 loaded trailers pushes the lightweight tractor forward under heavy braking, overcoming tire friction.

Q42A heavy-duty electric airport tugger trips on thermal cut-out within 20 minutes of towing aircraft baggage dollies. Root cause?

AnswerGross overload exceeding the tractor continuous drawbar pull rating, dragging mechanical parking brakes on trailers, or under-inflated solid-pneumatic drive tires dramatically increasing rolling resistance.

Q43What failure mode in an automated mechanical pin hitch allows towed trailers to uncouple accidentally during transit?

AnswerWorn spring-loaded hitch latch pin or failure of the secondary safety drop-pin interlock. Under dynamic vertical bouncing over dock plates, the loose hitch pin jumps out of the lunette ring eye.

Q44An electric tugger steering pulls heavily to the left under acceleration, requiring continuous operator fighting of the tiller. Why?

AnswerDifferential drive motor speed mismatch (dual-drive unit running with un-synchronized encoder feedback), or uneven drive tire wear (left drive tire diameter 15 mm smaller than right tire).

Q45Why do regenerative braking systems on heavy industrial tuggers shut off unexpectedly when descending steep ramps with a full battery?

AnswerBattery overvoltage protection. A 100% fully charged battery cannot accept regenerative energy without dangerously spiking DC bus voltage. The controller disengages regen, requiring friction hydraulic brakes to handle full descent.

Q46In a hospital pneumatic tube transport system, a medicine carrier capsule gets stuck halfway inside a 4th-floor ceiling pipe. How to locate and clear?

AnswerUse the central blower control software to read optical capsule passing sensor timestamps to identify the jammed pipe block. Switch high-power centrifugal exhausters into reverse pressure blast mode to blow the capsule backwards to the sending station.

Q47A pneumatic tube capsule arrives at the destination station with extreme supersonic velocity, violently smashing its plastic casing. Cause?

AnswerFailure of the receiving station air-cushion damper valve. The station must close an exhaust valve when the capsule approaches to compress a pocket of air ahead of the capsule, decelerating it smoothly to zero velocity.

Q48What causes a pneumatic capsule to lose driving speed and stall inside a long horizontal PVC tube run?

AnswerWorn felt or polyurethane glider rings on the capsule body. If the sealing rings wear down by >1.5 mm, compressed air slips past the capsule perimeter without generating the required pressure differential ($\Delta P = 0.3ext{ bar}$) to propel it.

Q49A pneumatic tube system diverter / multi-way junction switch jams, triggering a systemic system lockout. Root cause?

AnswerForeign debris or broken plastic capsule fragments wedged in the rotating tube slide mechanism, low compressed air pressure to the pneumatic shifting cylinders (<5 bar), or misaligned proximity limit switches.

Q50How does static electricity buildup inside non-conductive PVC pneumatic transport tubes create operational failures?

AnswerFriction of plastic capsule rings against dry PVC builds >25 kV electrostatic charges. Electrostatic attraction pulls dust into thick caked layers on tube walls, jamming capsules, while static discharges crash optical station sensors.

DOCK LEVELERS, VACUUM LIFTERS & HANDLING ATTACHMENTS

Q51A hydraulic dock leveler platform rises when the push button is held, but the front hinged lip fails to swing open and extend. Why?

AnswerLow hydraulic oil level (insufficient oil volume to fill the auxiliary lip cylinder), a jammed lip mechanical hinge pin, or defective lip sequence valve failing to shift pressure from main cylinder to lip cylinder at top of stroke.

Q52A dock leveler platform sinks under the weight of a loaded forklift, falling 100 mm below the truck bed. What failed?

AnswerInternal bypass leakage across the main hydraulic lift cylinder piston seals, or debris holding the hydraulic lowering check valve poppet slightly open under load.

Q53What is the safety function of a mechanical truck vehicle restraint (hook lock) on a loading dock bay?

AnswerIt mechanically hooks onto the truck rear underride guard (ICC bar) with 150 kN force, locking the trailer to the dock. This physically prevents 'Trailer Creep' (forklift momentum pushing the truck away from the dock, creating an open chasm).

Q54An inflatable dock shelter / seal fails to blow up when a container truck reverses into the bay. Root cause?

AnswerBlower motor thermal overload tripped, ripped vinyl air bag fabric dumping air to atmosphere, or the truck presence photo-eye sensor unaligned/blinded by road grime.

Q55A mechanical spring-loaded dock leveler snaps upward with violent speed when the hold-down chain is pulled. How to adjust?

AnswerThe mechanical main counterbalance spring tension is set too tight, or the ratchet hold-down brake band mechanism is worn and slipping. Adjust main spring compression bolts to achieve neutral balance.

Q56An automated vacuum sheet lifter handling smooth steel plates drops a 500 kg plate mid-air during rapid hoist acceleration. Why?

AnswerDynamic inertia acceleration force exceeded vacuum holding force ($F = m(g + a)$), suction cup lip cracked/worn allowing vacuum leakage under shear load, or vacuum reservoir check valve failed.

Q57A vacuum pump running on an industrial glass handling crane pulls only -40 kPa instead of nominal -85 kPa. Where to isolate?

AnswerIsolate system branch by branch using shut-off ball valves: inspect internal paper/wire vacuum filter cartridge for dust clogging, check for split polyurethane suction hoses, and check vacuum pump sliding carbon vanes for wear.

Q58An electro-permanent magnetic lifter fails to release a steel billet; even with demagnetization cycle commanded, the billet stays stuck. Remedy?

AnswerIncomplete capacitive discharge pulse during the demagnetization phase. The controller must fire an alternating, decaying AC current pulse train through the alnico/neodymium coils to randomize magnetic domains. Replace faulty discharge SCR.

Q59Why does handling textured diamond-plate steel with standard flat suction cups cause immediate vacuum failure?

AnswerAtmospheric air leakage through surface voids. Diamond tread patterns prevent continuous planar seal contact. Handling rough or patterned surfaces requires specialized cellular foam rubber vacuum pads or high-flow multi-stage vacuum ejectors.

Q60What safety factor is mandatory under ASME B30.20 for below-the-hook vacuum lifting and magnetic lifting devices?

AnswerVacuum lifting devices must maintain a minimum safety factor of 2:1 on holding force at minimum operating vacuum. Magnetic lifting devices must maintain a minimum breakaway force safety factor of 2:1 (battery-powered) or 3:1 (permanent/standard).

BATTERY CHARGING ROOMS, FLEET TELEMATICS & PREVENTATIVE MAINTENANCE

Q61A flooded lead-acid forklift battery emits a foul rotten-egg smell and the plastic casing bulges during charging. Hazard?

AnswerTHERMAL RUNAWAY & HYDROGEN GAS EXPLOSION RISK. The battery is severely overcharged or has a shorted internal lead cell. High current boils sulfuric acid electrolyte into toxic hydrogen sulfide ($H_2S$) and explosive hydrogen ($H_2$). Kill charger breaker immediately.

Q62An automated forklift battery charging room exhaust fan trips. What safety interlock must immediately shut down all chargers?

AnswerHydrogen gas detection sensor / ventilation airflow interlock switch. Lead-acid charging generates hydrogen gas. If airflow ceases and hydrogen exceeds 1% concentration (25% of LEL), all chargers must be electrically locked out to prevent catastrophic room explosions.

Q63A lithium-ion (Li-ion) forklift battery drops into emergency shutdown at 40% charge with error 'Cell Under-Voltage'. Why?

AnswerInternal cell imbalance. While average pack voltage represents 40% state of charge, one degraded or weak cell sagged below the critical 2.5V cutoff limit under heavy lift load, forcing the internal Battery Management System (BMS) to open contactors.

Q64Forklift telematics systems log multiple daily 'High-G Shock / Impact' events on Truck #7. What is happening in the facility?

AnswerAggressive driving, collision with racking, or high-speed transit over broken dock plates. Telematics tri-axial accelerometers trigger above 1.5–2.5 G forces, pinpointing reckless drivers or damaged concrete floor joints.

Q65Why must battery cable Euro-connectors (e.g., REMA / Anderson plugs) on high-amperage fast chargers be inspected for contact pitting weekly?

AnswerHigh insertion arcing. Unplugging connectors while the charger is actively pushing 150A burns and pits the silver-plated copper contact fingers. Pitted contacts create high contact resistance ($P = I^2 R$), melting the plastic connector housing into a fire.

Q66A forklift battery charging room shows a buildup of white corrosive residue on charger terminals and nearby metal surfaces within weeks of installation. What should be addressed?

AnswerInadequate ventilation allowing hydrogen and acid mist released during charging to accumulate and settle on surfaces. Verify the room meets required air-change ventilation standards for lead-acid battery charging, and install eyewash/neutralizing stations per safety code.

Q67A fleet telematics system reports a forklift as 'idle' for hours while operator logs show it was actively used during that period. What data issue should be investigated?

AnswerA malfunctioning or miscalibrated motion/ignition sensor failing to detect actual operation, or a firmware/connectivity issue preventing state updates from reaching the platform. Verify the telematics unit's sensor wiring and test state-change reporting against known operating periods.

Q68A battery charger repeatedly shows a fault code and refuses to begin charging a specific forklift battery, while other batteries charge normally on the same charger. What should be checked on the battery?

AnswerA battery with one or more shorted/open cells presenting abnormal voltage or impedance that the charger's diagnostic pre-check rejects as unsafe. Test individual cell voltages and specific gravity, and have the battery professionally tested/serviced before attempting to force a charge.

Q69A preventative maintenance program tracks forklift service by calendar interval, but several heavily used trucks fail components well before their scheduled service date. What should change in the PM strategy?

AnswerSwitch from calendar-based intervals to usage-based (hour-meter driven) intervals, since duty cycle varies significantly between trucks. Pull actual hour-meter or telematics usage data to set PM intervals proportional to real operating hours rather than fixed calendar dates.

Q70An opportunity-charging lithium-ion forklift battery shows reduced runtime after several months, even though it is charged frequently throughout each shift. What should be investigated?

AnswerSome capacity fade from cycling is normal, but first check whether the battery management system is allowed occasional full charge/discharge cycles for cell balancing — constant partial charging without periodic balancing can accelerate imbalance and apparent capacity loss. Review BMS balancing logs against manufacturer guidance.

📚 Buy Full Troubleshooting Q&A PDF — ₹99

You’ve read the first 70 questions here. Get the complete Troubleshooting Question Bank PDF with all questions and clear answers. One-time price: ₹99.

🛒 Buy PDF – ₹99