This manual covers the Caterpillar GC Series Forklift Trucks, including models GC15K, GC18K, GC20K, GC20K HP, GC25K, GC25K HP, and GC30K. These robust machines are engineered for reliable performance in demanding material handling environments, featuring Liquefied Petroleum Gas (LPG) engines such as the Caterpillar 4G63, 4G64, and 6G72, along with an LPG Fuel System that meets CARB Tier 1 standards. The series is built with quality components, including Powershift Transmissions, robust front and rear axles, and comprehensive hydraulic systems, ensuring durability and operational efficiency for a wide range of industrial applications. This Service Repair Manual provides detailed information essential for the maintenance, repair, and troubleshooting of your Caterpillar GC Series Forklift Truck. It includes extensive diagnostic procedures and diagnostic trouble codes (DTCs) for various systems, covering LPG, fuel, electrical, powertrain, axles, brakes, steering, and hydraulics. Furthermore, the manual offers comprehensive coverage of chassis and mast components, transmission, braking and steering systems, hydraulic components, mast systems, and forks. Maintenance sections feature interval and lubrication charts, while technical data includes dimensions, weights, tightening torques, and special service tools. Wiring diagrams and schematics for LPG and general systems are also provided to aid in accurate diagnostics and repairs.