Category:
Performance Sedan/Hatchback
Target Audience:
Enthusiasts, Rally Fans, Performance Car Owners
Competitors:
Mitsubishi Lancer Evolution, Honda Civic Type R (later generations), Volkswagen Golf GTI, Ford Focus RS
Performance Focus:
Legendary turbocharged boxer engine, Symmetrical All-Wheel Drive, performance-tuned suspension, driver-centric cockpit.
Rally Heritage:
Direct lineage from Subaru's World Rally Championship (WRC) successes, translating to robust and capable mechanicals.
Geographic Coverage:
North America (primarily), with some international applicability
Trim Levels Covered:
WRX STi (all variants)
Estimated Page Count:
~1500-2000 (typical for comprehensive factory service manuals of this era)
Type:
Factory Service Repair Manual (FSM)
Purpose:
Professional Technician and Advanced DIYer
Powertrain:
Engine (EJ257), Turbocharger System, Fuel System, Ignition System, Exhaust System, Engine Control System (ECU), Transmission (6-speed Manual), Drivetrain (AWD System, Differentials)
Chassis:
Suspension (Front & Rear), Steering System, Braking System (ABS, Performance Brakes), Wheels & Tires
Electrical:
Wiring Diagrams, Lighting, Instrumentation, HVAC Controls, Audio System, Power Accessories, Engine Management Sensors, Body Control Modules
Body:
Body Panels, Exterior Trim, Interior Trim, Seats, Doors, Windows, Roof (including sunroof if equipped), Bumpers
Maintenance:
Scheduled Maintenance, Oil Changes, Filter Replacements, Spark Plug Replacement, Fluid Checks & Replacements, Belt Inspections & Replacement
Repair:
Engine Overhaul, Turbocharger Rebuild/Replacement, Transmission Rebuild/Replacement, Suspension Component Replacement, Brake System Overhaul, Electrical Component Diagnosis & Repair, Body Panel Repair
Diagnostics:
OBD-II Diagnostics, Trouble Code Interpretation, Sensor Testing, Actuator Testing, System Troubleshooting Flowcharts
Specifications:
Torque Specifications, Clearances, Tolerances, Electrical Resistance Values, Pressure Readings
Depth:
Comprehensive: Covers basic maintenance to complete engine and transmission rebuilds, including detailed diagnostic procedures and wiring schematics.
Engine Type:
EJ257 - 2.5L Boxer-4, DOHC, 16-Valve, Turbocharged
Bore X Stroke:
99.5 mm x 79.0 mm
Horsepower:
300 hp @ 6000 rpm (SAE Net)
Torque:
300 lb-ft @ 4000 rpm (SAE Net)
Fuel Type:
Premium Unleaded Gasoline (91 Octane or higher recommended)
Injection System:
Sequential Multi-port Fuel Injection (MPI)
Turbocharger:
IHI VF39 (Water-cooled, Ball-bearing)
Type:
6-Speed Manual Transmission (TY856WN1AA)
Drivetrain:
Symmetrical All-Wheel Drive (AWD) with Driver Controlled Center Differential (DCCD)
Front Differential:
Viscous coupling limited-slip differential (VLSD)
Rear Differential:
Viscous coupling limited-slip differential (VLSD)
Length:
175.0 inches (Sedan), 174.4 inches (Wagon)
Height:
56.1 inches (Sedan), 55.3 inches (Wagon)
Ground Clearance:
5.6 inches
Curb Weight:
~3,175 - 3,260 lbs (depending on body style)
Gross Vehicle Weight Rating:
4,400 lbs
Towing Capacity:
Not Recommended
NHTSA Front Crash Test:
5-Star (Driver & Passenger) - 2004 Model Year
NHTSA Side Impact Crash Test:
5-Star (Front & Rear Occupant) - 2004 Model Year
IIHS Front Offset Crash Test:
Good
ABS:
Standard (4-wheel disc, vented front/rear)
Traction Control:
Standard
Stability Control:
Not Standard (VDC - Vehicle Dynamics Control became more widespread in later years)
Airbags:
Front Dual-Stage Airbags, Front Side-Impact Airbags
Seatbelts:
Pretensioner & Force Limiter Front Seatbelts, LATCH System for Child Seats
Audio System:
Factory AM/FM/CD Player with 6 speakers. Optional subwoofer available.
Display:
Basic digital display for clock, temperature, and system status. No central infotainment screen as found in modern vehicles.
Keyless Entry:
Available on some trims/packages
Automatic Climate Control:
Available on some higher trims/packages
Bluetooth:
Not available from the factory
Usb Port:
Not available from the factory
Oil Change Interval:
Every 3,000-5,000 miles or 6 months (whichever comes first), depending on driving conditions. Subaru typically recommends 3,750 miles for severe use.
Engine Air Filter:
Inspect every 15,000 miles, replace as needed. Often sooner for spirited driving or dusty conditions.
Cabin Air Filter:
Replace every 15,000-30,000 miles or annually.
Spark Plugs:
Replace every 60,000 miles (NGK Iridium recommended).
Timing Belt:
This engine uses a timing *belt*. Replace every 105,000 miles or 105 months. Inspect tensioners and water pump at the same time.
Engine Oil:
SAE 5W-30 Synthetic (API SG, SH, SJ, SL, or SM rated). Check manual for specific viscosity approvals.
Transmission Fluid:
Subaru Extra-S Gear Oil or equivalent API GL-5 for 6MT. Manual specifies Subaru Extra-S. Capacity: ~3.2 liters.
Differential Fluid:
API GL-5. Front: ~1.0 liter, Rear: ~1.3 liters. Subaru Extra-S recommended.
Coolant:
Subaru Super Coolant (Blue) or equivalent 50/50 mix. Capacity: ~7.9 liters.
Head Gaskets:
While EJ257 engines are generally more robust than earlier EJ25s, head gasket failures can still occur due to high cylinder pressures and thermal stress. The 2004 model year is less prone than some earlier ones, but still a consideration.
Ring Land Failure:
Can occur on stock or modified engines with aggressive tuning or inadequate fueling, leading to piston damage.
Clutch Wear:
High-performance nature of the car and potential for spirited driving can lead to accelerated clutch wear. OEM clutch is robust but not indestructible.
Turbo Failure:
The VF39 turbo is known to be reliable but can fail prematurely if oil starvation or contamination occurs, or due to excessive boost from modifications.
Car And Driver 10Best:
The Subaru Impreza WRX (non-STi) was a consistent contender and often featured on Car and Driver's 10Best lists in earlier generations, establishing its performance credibility.
Motor Trend:
Frequently praised by automotive journalists for its all-weather performance, handling, and accessible turbo power.
Performance Testing:
The manual provides detailed specifications and procedures crucial for maintaining and optimizing the vehicle's high-performance capabilities.
