Vehicle Segment:
Performance Compact Sedan/Wagon
Competitors 2004:
Mitsubishi Lancer Evolution VIII, Ford Focus SVT, Volkswagen GTI
Unique Selling Proposition:
Symmetrical All-Wheel Drive, turbocharged boxer engine, rally heritage
Performance Focus:
Engineered for high performance and handling, with a strong emphasis on driver engagement.
Manual Value:
Indispensable resource for owners and technicians seeking to maintain and repair the complex STI platform.
Engine:
Engine mechanical, lubrication, cooling, fuel injection, ignition, emissions control, turbocharger system
Transmission:
Manual transmission (6-speed), clutch, driveline, limited-slip differentials (front, center, rear)
Brakes:
Front and rear disc brakes (Brembo calipers standard on STI), ABS, brake hydraulics, parking brake
Suspension:
Front MacPherson struts, rear multi-link independent suspension, springs, dampers, sway bars, alignment specifications
Steering:
Power assisted rack and pinion steering, steering column, tie rods
Electrical:
Battery, charging system, starting system, lighting, instrumentation, audio system, immobilizer, ECU wiring diagrams
Body:
Body panels, doors, hood, trunk, bumpers, interior trim, glass, locks, hinges
HVAC:
Heating, ventilation, air conditioning system, refrigerant, controls
Diagnostics:
OBD-II diagnostics, trouble codes, sensor data interpretation, testing procedures
Maintenance:
Routine maintenance, oil changes, filter replacements, fluid checks and changes, belt inspection and replacement, spark plug replacement
Repair:
Engine component replacement (pistons, rods, valves), turbocharger rebuild, transmission overhaul, brake caliper replacement, suspension component replacement, electrical component repair
Troubleshooting:
Step-by-step diagnostic procedures for common and uncommon faults, electrical circuit tracing, mechanical system diagnosis
Installation:
Component installation and removal, accessory fitting, timing belt installation
Depth Level:
Comprehensive (from basic maintenance to complete engine and transmission rebuilds)
Diagnostic Complexity:
Advanced diagnostic routines, including oscilloscope interpretation and component testing
Wiring Diagrams:
Detailed and specific wiring schematics for all major systems
Engine Type:
2.5L DOHC 16-valve turbocharged horizontally opposed (boxer) 4-cylinder
Horsepower:
300 hp @ 6000 rpm (SAE Net)
Torque:
300 lb-ft @ 3500 rpm (SAE Net)
Fuel Type:
Premium Unleaded Gasoline (91 octane or higher recommended)
Fuel Delivery:
Sequential multi-point fuel injection with electronic throttle control
Turbocharger:
IHI VF39 Ball Bearing Turbocharger with Top-Mount Intercooler
ECU Type:
Denso ECU (specific part number for reference in manual)
NHTSA Front Crash Rating:
4 Stars
NHTSA Side Crash Rating:
4 Stars
IIHS Frontal Offset Rating:
Good
ABS:
Standard Anti-lock Braking System
AWD:
Standard Symmetrical All-Wheel Drive
Airbags:
Front dual-stage airbags, front side-impact airbags
Seatbelts:
Three-point seatbelts with pretensioners and load limiters
Oil Change Interval:
Every 3,750 miles or 3 months (severe duty) / 7,500 miles or 6 months (normal duty)
Timing Belt Replacement Interval:
105,000 miles or 7 years (critical for EJ257 engine)
Engine Oil Type:
0W-30 or 5W-30 Synthetic (API SN or higher, ILSAC GF-5 or higher recommended)
Engine Oil Capacity:
4.8 US quarts (with filter change)
Coolant Type:
Subaru Super Coolant (Blue) or equivalent Phosphate-Free Long Life Coolant
Piston Ringland Failure:
Common issue with EJ257 engines under aggressive tuning or sustained high loads; manual provides diagnostic and repair procedures.
Clutch Wear:
Due to performance nature, clutch longevity can be impacted; manual covers clutch inspection and replacement.
Turbocharger Failure:
Improper break-in or lack of oil changes can lead to turbo issues; manual details inspection and rebuilds.
Sport Compact Awards 2004:
Frequently cited as a benchmark performance compact by automotive publications of the era.
Car And Driver 10 Best:
While not explicitly listed for 2004, the Impreza WRX (non-STI) was a consistent contender on '10Best' lists in preceding years, establishing the model's performance credentials.
Emissions Compliance:
Meets EPA and CARB emissions standards for the 2004 model year; manual details emission control systems.
