# Guide to Common Fault Diagnosis and Maintenance of Rough Terrain Forklifts

I. Typical Faults of the Power System Difficulty in engine starting — Fault symptoms: Cold start time greater than 15 seconds; white smoke from the exhaust pipe (unburned diesel). Repair plan: Preheat system upgrade (install an ether starting device for -30°C environments); high-pressure fuel pump calibration (injection pressure error ±0.5 MPa). Power decline — Root cause analysis: Turbocharger oil leakage (causing insufficient boost pressure); clogged air filter (intake volume drops by more than 30%). On-site inspection: Use a vacuum gauge to measure intake pipe negative pressure (normal value 25-30 kPa); use an infrared thermal imager to check exhaust temperature (a temperature difference greater than 50°C among cylinders is abnormal). II. Common Faults of the Hydraulic System Weak lifting — Three-step diagnosis method: Test no-load lifting speed (standard value ±10%); check the main relief valve setting pressure (compare with the nameplate); detect cylinder internal leakage (measure settlement during extension). Typical cases: Multi-way valve spool wear (replacement required when fit clearance is greater than 0.03 mm); hydraulic oil emulsification (water content greater than 1000 ppm). High hydraulic oil temperature — Cooling system inspection checklist: Radiator fin pass-through rate (cleaning mandatory when blockage is greater than 40%); fan belt tension (deflection 10-15 mm); oil viscosity (replacement required when less than 32 cSt at 40°C). III. Travel System Faults Four-wheel drive failure — Transfer case inspection points: Check solenoid valve resistance (standard value 28-32 Ω); measure clutch plate thickness (replace when less than 3.5 mm). Quick judgment method: Measure torque transmission efficiency with the front axle lifted (less than 85% is abnormal). Abnormal tire wear — Alignment parameter standards: | Parameter | Standard value | Allowable deviation | | Toe-in angle | 3-5 mm | ±1 mm | | Camber angle | 0.5-1° | ±0.3° | | Kingpin caster angle | 2-4° | ±0.5° | Recommended adjustment tools: Laser aligner (accuracy ±0.1°); steering torque detection wrench. IV. Electrical System Faults Dashboard alarm — Fault code interpretation: P0087: Low fuel pressure fault (check the fuel transfer pump); U0121: CAN bus communication interruption (measure terminating resistor). Circuit repair techniques: Use an oscilloscope to detect sensor signals (such as the crankshaft position sensor); harness impedance test (standard less than 0.5 Ω/10 m). Lighting system faults — Waterproofing solutions: Apply silicone grease to headlight connectors (temperature resistance -40 to 200°C); upgrade harness corrugated tubing (flame retardant rating UL94 V-0). V. Structural Component Repair Standards Mast deformation repair — Correction process: Laser measurement of guide rail straightness (tolerance ≤1 mm/m); local heating correction (temperature control 650 ± 50°C). Safety test: 110% rated load test (hold for 5 minutes). Abnormal noise at articulated parts — Repair kit replacement standards: Pin shaft diameter wear greater than 0.5 mm; bronze bushing clearance greater than 1.2 mm. Recommended repair tools — Specialized equipment: Hydraulic tester (simultaneous flow/pressure detection); wireless cylinder pressure tester. Intelligent diagnosis: Fault diagnostic instrument (supports J1939 protocol); thermal imaging phone accessory (detects electrical hot spots). Repair safety rules: Depressurize the hydraulic system before operation; lifting devices must be mechanically locked; disconnect the battery negative terminal first. Typical case library (scan the QR code to view): Turbocharger blade fracture analysis; emergency handling of multi-way valve sticking; record of CAN bus interference troubleshooting. By establishing a three-dimensional fault tree of "symptom-cause-solution," the first-time repair rate can be increased by more than 80%. It is recommended to use a fault simulator every quarter to conduct skills training and maintain the technical sharpness of the repair team.