🏷️ Basic Information

Make:

Subaru

Model:

Impreza WRX STI

Model Variant:

WRX STI

Years Covered:

2004-2005

Chassis Codes:

GDB (Specific variants for STI)

👋 Introduction

Vehicle Segment:

Performance Compact Sedan/Wagon, Rally-bred Sports Car.

Key Competitors:

Mitsubishi Lancer Evolution, Ford Focus RS, Honda Civic Type R (in broader performance segments).

Vehicle Highlights:

Iconic turbocharged boxer engine, advanced Symmetrical All-Wheel Drive, performance-tuned suspension, DCCD, potent braking system, rally heritage.

Diy Enablement:

Empowers owners to perform a wide range of repairs and maintenance, saving on labor costs and fostering a deeper understanding of their vehicle.

📋 Manual Details

General Coverage:

Comprehensive repair and maintenance for the Subaru Impreza WRX STI.

Specific Systems:

Engine, Drivetrain, Suspension, Steering, Brakes, Electrical System, HVAC, Bodywork, Emissions.

Estimated Page Count:

Approximately 2000+ pages (typical for comprehensive factory service manuals of this era).

Manual Type:

Factory Service Manual (FSM) / Repair Manual

Language:

English

Digital Format:

PDF

📖 Manual Coverage

Engine Management:

Detailed diagnostics and repair procedures for the EJ257 engine, including ECU functions, sensors, actuators, and fuel injection systems.

Drivetrain And AWD:

In-depth coverage of the symmetrical All-Wheel Drive system, including DCCD (Driver Controlled Center Differential), viscous coupling unit, front/rear differentials, and gearbox maintenance/overhaul.

Suspension And Steering:

Complete information on the performance-tuned suspension, including strut assembly removal/installation, alignment procedures, power steering system diagnostics, and steering rack overhaul.

Braking System:

Detailed procedures for the performance Brembo braking system, including rotor and pad replacement, caliper servicing, brake fluid bleeding, and ABS system diagnostics.

Electrical System:

Comprehensive wiring diagrams, troubleshooting guides for lighting, starting/charging systems, infotainment, and various control modules.

Routine Maintenance:

Oil changes, filter replacements (oil, air, fuel), coolant flush, spark plug replacement, belt inspection and replacement.

Engine Repair:

Top-end rebuilds (cylinder heads), bottom-end overhauls, turbocharger diagnostics and replacement, intercooler system servicing.

Transmission Overhaul:

Detailed steps for clutch replacement, gearbox disassembly and reassembly, transfer case servicing, and differential rebuilds.

Troubleshooting Diagnostics:

Systematic diagnostic trees and fault code interpretation for common and complex issues.

Depth Of Coverage:

Covers everything from basic fluid checks and filter changes to complete engine and transmission rebuilds, including component-level diagnostics and specifications.

📊 Manual Specifications

File Type:

PDF

Searchability:

Searchable text for quick information retrieval.

Printability:

High-resolution, optimized for clear printing of text and diagrams.

Zoom Capability:

Excellent zoom capability for detailed inspection of diagrams and text.

Binding Description:

N/A (Digital PDF format)

Paper Description:

N/A (Digital PDF format)

Operating Systems:

Compatible with all Windows and macOS operating systems.

⚙️ Engine Specifications

Engine Code:

EJ257

Engine Type:

2.5L DOHC turbocharged flat-four boxer engine

Horsepower Output:

300 hp @ 6000 rpm (approx.)

Torque Output:

300 lb-ft @ 4000 rpm (approx.)

Fuel Delivery:

Multi-point fuel injection (MPI) with top-feed injectors.

Recommended Fuel:

Premium Unleaded Gasoline (91 octane or higher)

Coolant Type:

Subaru Super Coolant (Blue) or equivalent silicate-free OAT coolant.

Oil Type:

Synthetic SAE 0W-30 or 5W-30

Oil Capacity:

4.8 US quarts (4.5 Liters) with filter

Turbo Model:

IHI VF39 (typical for this generation)

🔧 Transmission

Transmission Type:

6-speed Manual Transmission

Optional Transmission:

N/A (STI models were exclusively manual)

Dccd System:

Driver Controlled Center Differential (DCCD) for adjustable torque split.

Transmission Fluid Type:

Subaru Extra Synchros 75W-90 GL-5 (gearbox) / Subaru Extra Synchros 75W-90 GL-5 (transfer/rear diff, though separate fill often specified).

Clutch Fluid:

DOT 3 or DOT 4 brake fluid

📐 Dimensions

Length:

4415 mm (173.8 in)

Width:

1770 mm (69.7 in)

Height:

1440 mm (56.7 in)

Wheelbase:

2625 mm (103.3 in)

Curb Weight:

Approx. 1450-1500 kg (3197-3307 lbs)

Gross Vehicle Weight Rating:

Not typically specified in detail for performance models, but implied by chassis load capacity.

Standard Wheel Size:

17 x 7.5 inches

Standard Tire Size:

225/45R17

Bolt Pattern:

5x100 mm

🛡️ Safety Features

NHTSA Front Impact Rating:

4/5 Stars (for comparable 2004 Impreza models, STI specific may vary slightly)

IIHS Side Impact Rating:

Good (for comparable 2004 Impreza models)

ABS:

Standard Anti-lock Braking System (ABS)

Traction Control:

Standard Traction Control System (TCS) and Vehicle Dynamics Control (VDC).

Airbags:

Front airbags, side airbags, and curtain airbags (depending on specific market/trim).

Seat Belts:

3-point seatbelts with pretensioners and force limiters.

Body Structure:

Reinforced unibody construction with crumple zones.

💡 Technology Features

Audio System:

Factory AM/FM/CD player with optional premium audio.

Display System:

Basic digital/analog instrumentation, no advanced touchscreen infotainment.

Cruise Control:

Standard electronic cruise control.

Usb Aux Input:

Generally not equipped with factory USB/Aux inputs; aftermarket solutions common.

🔧 Maintenance

Oil Change Interval:

Every 3,000-5,000 miles or 3-6 months, especially under spirited driving conditions.

Spark Plug Replacement:

Approximately every 60,000 miles (refer to manual for specific type and gap).

Timing Belt Replacement:

Approximately every 105,000 miles or 7 years (critical maintenance item for EJ engines).

Brake Fluid Type:

DOT 3 or DOT 4

Power Steering Fluid:

Subaru Genuine Power Steering Fluid or Dexron III/Mercon compatible ATF.

Coolant Capacity:

Approx. 7.1 US quarts (6.7 Liters)

Piston Ring Land Failure:

Common issue in early EJ257 engines, particularly with aggressive tuning or poor maintenance. Manual provides diagnostics and repair procedures.

Turbo Seal Wear:

Turbocharger seals can wear, leading to oil consumption. Manual covers inspection and replacement.

Clutch Wear:

High-performance driving can accelerate clutch wear. Manual provides replacement procedures.

Suspension Component Wear:

Bushings and bearings can wear over time, affecting handling. Manual details replacement.

📚 Vehicle History

Rally Connection:

Subaru's deep roots in the World Rally Championship (WRC), directly influencing the Impreza WRX STI's development and reputation.

Gc8 To Gd Transition:

This generation (GD chassis) marked a significant design and engineering evolution from the previous GC8 generation.

Sti Distinction:

The STI variant represents the pinnacle of the Impreza line, featuring a more powerful engine, upgraded drivetrain, and enhanced chassis components compared to the standard WRX.

Manufacturing Location:

Japan (Subaru's primary manufacturing base)

🏆 Awards & Recognition

Car And Driver 10Best:

While the STI itself might not have been on the 10Best list, the Impreza platform often featured highly in performance car discussions and comparisons.

Rally Championships:

Numerous WRC titles and championships secured by Subaru factory rally cars, directly validating the Impreza platform's performance capabilities.

Performance Car Status:

Consistently recognized as a benchmark for affordable, high-performance all-wheel-drive sports sedans.