🏷️ Basic Information

Make:

Subaru

Model:

Impreza WRX STI

Year:

2004

Chassis Code:

GDB

Engine Code:

EJ257

👋 Introduction

Segment:

Performance Compact Sedan/Wagon

Target Audience:

Enthusiast drivers, rally sport fans, performance vehicle owners.

Key Competitors:

Mitsubishi Lancer Evolution, Subaru WRX (non-STI variants), Honda Civic Type R (later generations), Volkswagen Golf GTI.

Unique Selling Proposition:

Legendary Subaru Symmetrical All-Wheel Drive system with Driver Controlled Center Differential (DCCD), robust EJ257 engine, rally-bred heritage, iconic styling.

Performance Focus:

Designed for spirited driving and track performance.

AWD System:

Symmetrical AWD with DCCD for optimal traction and handling.

Turbocharged Engine:

High-output EJ257 boxer engine with a twin-scroll turbocharger.

Advanced Braking:

Brembo braking system for superior stopping power.

Rally Heritage:

Direct lineage to Subaru's successful World Rally Championship (WRC) campaigns.

📋 Manual Details

Coverage Type:

Full Service & Repair Workshop

Estimated Pages:

1500-2000+

Type:

Factory Service Manual

Language:

English

Format:

Digital Download (PDF)

📖 Manual Coverage

Engine Mechanical:

Complete disassembly, inspection, repair, and reassembly of the EJ257 engine.

Engine Electrical:

Ignition system, fuel injection system, starting system, charging system, sensors, actuators, ECU.

Transmission:

6-speed manual transmission (TY856WB1CA), clutch system, differential maintenance and repair.

Drivetrain:

All-Wheel Drive (AWD) system, center differential, front and rear differentials, driveshafts, axles.

Suspension:

Front and rear suspension components, struts, springs, control arms, sway bars, alignment procedures.

Brakes:

Front Brembo 4-piston calipers and rear Brembo 2-piston calipers, ABS system, brake fluid, lines, rotors, pads.

Steering:

Power steering system, steering rack, tie rods, steering column.

Cooling System:

Radiator, fans, water pump, thermostat, coolant types and capacities.

Fuel System:

Fuel pump, injectors, fuel lines, fuel filter, evaporative emissions control (EVAP) system.

Exhaust System:

Catalytic converter, mufflers, O2 sensors, turbocharger exhaust components.

Electrical Body:

Lighting systems, power windows, central locking, mirrors, interior lighting, wiring diagrams.

HVAC:

Heating, Ventilation, and Air Conditioning (HVAC) system, refrigerant, components, troubleshooting.

Body Interior:

Interior trim removal and installation, seat removal, dashboard components.

Body Exterior:

Panel removal and installation, bumper replacement, fender repair, door adjustments.

Routine Maintenance:

Oil changes, filter replacements, spark plug replacement, fluid checks and top-offs.

Troubleshooting:

Diagnostic flowcharts for common problems, DTC (Diagnostic Trouble Code) interpretation.

Engine Overhaul:

Detailed steps for engine rebuild, including torque specifications, piston ring gap, bearing clearance.

Turbocharger Service:

Inspection, repair, and replacement procedures for the twin-scroll turbocharger.

Transmission Rebuild:

Complete guide to disassembling, inspecting, and reassembling the 6-speed manual gearbox.

Clutch Replacement:

Step-by-step instructions for replacing the clutch assembly.

Brake System Overhaul:

Pad and rotor replacement, caliper service, brake bleeding procedures.

Suspension Component Replacement:

Strut, shock absorber, ball joint, and bushing replacement.

Wheel Alignment:

Alignment specifications and procedures.

Electrical Diagnostics:

Wiring diagrams, connector pinouts, troubleshooting electrical faults.

HVAC System Repair:

Component testing, refrigerant charging, leak detection.

Body Panel Repair:

Procedures for dent repair, panel alignment, and fastener specifications.

Depth Level:

Comprehensive factory-level detail

Detail Level:

From basic fluid changes to complete engine and transmission rebuilds.

Diagnostic Capabilities:

Includes diagnostic procedures, fault code lookup, and sensor data interpretation.

Wiring Diagrams:

Detailed electrical schematics for all major systems.

Torque Specifications:

Precise torque values for all critical fasteners.

Special Tools:

Identification of specialized tools required for specific procedures.

📊 Manual Specifications

Format:

PDF

Searchable Text:

Yes, for easy navigation and information retrieval.

Image Resolution:

High-resolution, clear diagrams and images.

Binding:

Not Applicable (Digital)

Paper Type:

Not Applicable (Digital)

⚙️ Engine Specifications

Engine Type:

Horizontally-opposed (Boxer) turbocharged 4-cylinder

Displacement:

2.5 Liters (2457 cc)

Bore X Stroke:

99.5 mm x 79.0 mm

Compression Ratio:

8.2:1

Valve Train:

DOHC (Dual Overhead Camshafts), 16 valves

Fuel Delivery:

Multi-point fuel injection with Denso 650cc injectors (factory specification)

Horsepower:

300 hp @ 6000 rpm (SAE Net)

Torque:

300 lb-ft @ 4000 rpm (SAE Net)

Redline:

7000 rpm

Turbocharger:

IHI VF37 twin-scroll turbocharger

Fuel Type:

Premium Unleaded Gasoline (91 octane or higher recommended)

🔧 Transmission

Type:

6-speed Manual Transmission (Subaru TY856WB1CA)

Optional Type:

None available for STI model in 2004

Driver Controlled Center Differential:

DCCD system allowing manual adjustment of center differential locking.

Limited Slip Differentials:

Front and rear helical limited-slip differentials.

First Gear:

3.636

Second Gear:

2.200

Third Gear:

1.541

Fourth Gear:

1.121

Fifth Gear:

0.972

Sixth Gear:

0.731

Reverse:

3.545

Final Drive Ratio:

3.545

Manual Transmission Fluid:

Subaru Extra-S Gear Oil API GL-5 75W-90 (or equivalent high-quality synthetic)

📐 Dimensions

Length:

177.1 inches (4498 mm)

Width:

69.7 inches (1770 mm)

Height:

56.1 inches (1425 mm)

Wheelbase:

104.0 inches (2640 mm)

Front Track:

60.2 inches (1529 mm)

Rear Track:

59.6 inches (1514 mm)

Ground Clearance:

5.6 inches (142 mm)

Curb Weight:

3296 lbs (1495 kg)

Gross Vehicle Weight Rating:

4277 lbs (1940 kg)

Towing Capacity:

Not Recommended

Trunk Volume:

11.3 cubic feet (Sedan)

🛡️ Safety Features

NHTSA Front Impact Driver:

Not explicitly rated for 2004 model year by NHTSA in the same format as later years, but generally considered robust.

NHTSA Front Impact Passenger:

Not explicitly rated for 2004 model year by NHTSA in the same format as later years, but generally considered robust.

IIHS Frontal Offset:

Good (for similar models and era)

ABS:

4-wheel Anti-lock Braking System

Ebd:

Electronic Brake-force Distribution

Traction Control:

Yes

Stability Control:

Not standard on 2004 model

Airbags Driver:

Frontal Airbags

Airbags Passenger:

Frontal Airbags

Airbags Side:

Optional Front Side-Impact Airbags

Seatbelts:

3-point front and rear seatbelts with pretensioners and load limiters

Child Anchors:

LATCH (Lower Anchors and Tethers for Children) system

💡 Technology Features

Head Unit:

Standard Subaru AM/FM stereo with CD player. Optional premium sound system may be available on some trims.

Speaker System:

Typically 4 or 6 speakers, depending on trim level.

Cruise Control:

Standard

Anti Theft:

Factory immobilizer system

Aux Input:

Not standard, may require aftermarket modification or be present on premium units.

Bluetooth:

Not available from factory on 2004 model.

🔧 Maintenance

Oil Change Interval:

Every 3,750 miles (6,000 km) or 3 months, whichever comes first. Under severe driving conditions, more frequent changes are recommended.

Engine Air Filter:

Inspect every 15,000 miles (24,000 km), replace as needed. Replace every 30,000 miles (48,000 km) if driving in dusty conditions.

Cabin Air Filter:

Replace every 15,000 miles (24,000 km) or 12 months.

Spark Plugs:

Replace every 30,000 miles (48,000 km). Use iridium or platinum tip plugs.

Transmission Fluid Change:

Every 30,000 miles (48,000 km) for manual transmission.

Differential Fluid Change:

Every 30,000 miles (48,000 km) for front and rear differentials.

Coolant Flush:

Every 30,000 miles (48,000 km) or 24 months.

Timing Belt:

This engine uses a timing *belt*. Replacement is recommended every 105,000 miles (168,000 km) or 7 years, whichever comes first. The manual will detail the procedure.

Engine Oil:

SAE 5W-30, API SL or SM, ACEA A3/B3 or A3/B4 certified (Subaru Synthetic recommended)

Coolant:

Subaru Super Coolant (Blue) or equivalent (50/50 mix with distilled water)

Brake Fluid:

DOT 3 or DOT 4

Power Steering Fluid:

Subaru Genuine Power Steering Fluid or DEXRON III/Mercon ATF

Headgaskets:

While the EJ257 is more robust than earlier EJ25s, head gasket failures can still occur, especially with modified vehicles. The manual will cover inspection and replacement.

Piston Ring Land Failure:

Can occur in high-mileage or heavily modified engines. Proper maintenance and avoiding pre-ignition are key. The manual provides specs for inspection.

Clutch Wear:

Performance driving can accelerate clutch wear. The manual details clutch inspection and replacement.

Turbocharger Wear:

Oil degradation or contamination can damage the turbocharger's oil seals and bearings. Regular oil changes are crucial.

Suspension Component Wear:

Bushings and bearings in the suspension can wear over time, leading to noise and handling degradation.

📚 Vehicle History

Company Origin:

Founded in 1919 as Fuji Heavy Industries, rebranded as Subaru Corporation in 2017. Known for its horizontally-opposed engines and Symmetrical All-Wheel Drive.

Impreza Introduction:

The Subaru Impreza was first introduced in 1992. The WRX (World Rally eXperimental) variant debuted in 1992, and the higher-performance STI (Subaru Tecnica International) version followed in 1994.

Gc8 Platform:

The 2004 Impreza WRX STI belongs to the 'GC8' platform, specifically the GDB generation, which was produced from 2000-2007. This generation marked significant styling and engineering advancements.

2004 Updates:

The 2004 model year brought a significant facelift ('Bugeye' to 'Blobeye') to the GC8 platform, introducing new headlights, front bumper, and an updated interior. Mechanically, it received the potent EJ257 engine in North America and the 6-speed manual transmission.

Manufacturing Location:

Ota City, Gunma Prefecture, Japan

Production Years For Model:

2004 - 2007 (GDB Generation)

🏆 Awards & Recognition

Car And Driver 2004:

Named to Car and Driver's '10Best' list for 2004.

Rally Success:

Subaru WRX STI has a decorated history in motorsports, particularly in the World Rally Championship (WRC), which heavily influenced its design and engineering.

Enthusiast Magazine Ratings:

Consistently praised by automotive journalists for its performance, handling, and AWD capabilities.

Emissions Standards:

Meets U.S. EPA and CARB emissions standards for 2004.