Welcome to the factory service manual for the 2004 Subaru Impreza WRX STI, a high-performance compact sedan renowned for its rally-bred heritage and exceptional all-wheel-drive capabilities. This model, part of the GDB generation, is celebrated for its potent 2.5L turbocharged Boxer engine, delivering approximately 300 horsepower and 300 lb-ft of torque, paired with a precise 6-speed manual transmission and Subaru's signature Symmetrical All-Wheel Drive system featuring a Driver Controlled Center Differential (DCCD). Its engineering emphasizes agile handling and a direct connection to the road, making it a standout in its class and a favorite among driving enthusiasts. This comprehensive manual provides in-depth coverage for all repairs, from routine maintenance to complex overhauls. You will find detailed procedures for the engine, transmission (both manual and automatic variants), drivetrain, suspension, brakes, steering, and electrical systems, including extensive wiring diagrams. The manual also covers body interior and exterior components, climate control, and safety restraint systems. With step-by-step instructions, diagnostic guides, and exploded diagrams, this resource is an indispensable tool for owners and technicians seeking to maintain, troubleshoot, and repair the 2004 Subaru Impreza WRX STI with accuracy and efficiency.