2004 Subaru Impreza Factory Service Workshop Repair Manual STI Engine H4SO Engine H4DOTC Engine Transmission CHASSIS BODY Wiring

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🏷️ Basic Information Identification Make: Subaru Model: Impreza Year: 2004 Trim Level: WRX STI Engine Variants Covered: • STI (EJ207/EJ257) • H4SO (Naturally Aspirated EJ20/EJ25) • H4DOTC (Turbocharged EJ20/EJ25) Codes Chassis Code: GDB 👋 Introduction Market Position Positioning: The 2004 Subaru Impreza, particularly the WRX STI variant, occupied a prominent position in the enthusiast compact performance car market, known for its rally-inspired engineering, all-wheel-drive capabilities, and potent turbocharged engines. Competitive Analysis Competitors: Competed against vehicles like the Mitsubishi Lancer Evolution, Volkswagen Golf GTI, Honda Civic Si, and Ford Focus SVT, differentiating itself with its standard Symmetrical All-Wheel Drive and boxer engine configuration. Key Features Performance Highlights: Turbocharged Boxer engines, Symmetrical All-Wheel Drive, sport-tuned suspension, advanced driver-controlled center differential (DCCD) on STI models, and a robust chassis. Manual Value Utility For Owners: An indispensable resource for owners seeking to perform maintenance, diagnose issues, or undertake repairs, enabling them to maintain the performance and longevity of their vehicle. 📋 Manual Details Coverage Areas Major Systems: • Engine (STI, Naturally Aspirated, Turbocharged) • Transmission (Manual, Automatic - though emphasis on Manual for STI) • Chassis (Suspension, Steering, Brakes, Drivetrain) • Body (Exterior and Interior) • Electrical System (Wiring Diagrams, Components, Diagnostics) Page Count Estimated Pages: 1000+ Manual Type Type: Factory Service Manual / Workshop Repair Manual Language Language: English Format Format: PDF Download 📖 Manual Coverage Systems Covered Powertrain: Detailed coverage of EJ207/EJ257 STI engines (including turbocharger system, fuel injection, ignition, emissions), EJ20/EJ25 naturally aspirated engines, and EJ20/EJ25 turbocharged engines. Comprehensive transmission information for manual transmissions, including clutch, gearbox, differential, and AWD system. Suspension And Steering: Front and rear suspension (MacPherson strut front, multi-link rear), steering system (rack and pinion), wheel alignment specifications, shock absorber and spring replacement procedures. Braking System: Front and rear disc brakes, ABS system, brake fluid specifications, caliper and rotor replacement, brake bleeding procedures. STI specific Brembo brake system details. Electrical System: Complete wiring diagrams for all vehicle systems, ECU pinouts, component locations, diagnostic procedures for electrical faults, lighting, audio system, power accessories, and safety systems. Body And Interior: Body panel removal and installation, door mechanisms, interior trim, seat removal, glass replacement, crash structure details. Procedures Included Diagnostics And Troubleshooting: Systematic troubleshooting charts for common issues, DTC (Diagnostic Trouble Code) interpretations, and diagnostic flowcharts for engine, transmission, and electrical systems. Maintenance: Routine maintenance tasks such as oil changes, filter replacements, spark plug replacement, coolant flush, brake inspections, and belt inspections. Repair And Overhaul: Detailed step-by-step instructions for major component overhauls, including engine rebuilds (pistons, rings, bearings, cylinder heads), transmission rebuilds, clutch replacement, brake system overhauls, and suspension component replacement. Special Tools And Jigs: Identification and usage guidelines for specific tools required for Subaru Impreza repairs and maintenance, including specialized engine and transmission tools. Technical Depth Depth: Comprehensive, covering everything from basic maintenance and fluid checks to complete engine and transmission rebuilds, advanced electrical diagnostics, and chassis component overhauls. Suitable for professional technicians and advanced DIY enthusiasts. 📊 Manual Specifications File Format File Type: PDF Searchability: Searchable text content for quick information retrieval. Printability: Printable pages for on-the-job reference. Print Quality Image Resolution: High-resolution diagrams, illustrations, and photographs. Binding Type Binding: N/A (Digital Download) Paper Type Paper: N/A (Digital Download) ⚙️ Engine Specifications Primary Engine Sti Engine Code: EJ257 (North American Market), EJ207 (JDM/European Market) Sti Engine Type: Intercooled Turbocharged, Horizontally Opposed (Boxer), DOHC, 16-valve Sti Displacement: 2.5 Liters (EJ257) / 2.0 Liters (EJ207) Sti Horsepower: Approx. 300 hp (STI) Sti Torque: Approx. 300 lb-ft (STI) Naturally Aspirated Engine Naturally Aspirated Engine Code: EJ253 (e.g., 2.5 RS) Naturally Aspirated Engine Type: Naturally Aspirated, Horizontally Opposed (Boxer), SOHC (some variants), DOHC (some variants), 16-valve Naturally Aspirated Displacement: 2.5 Liters Naturally Aspirated Horsepower: Approx. 165-170 hp Turbocharged Engine Turbocharged Engine Code: EJ255 (e.g., WRX) Turbocharged Engine Type: Intercooled Turbocharged, Horizontally Opposed (Boxer), DOHC, 16-valve Turbocharged Displacement: 2.5 Liters Turbocharged Horsepower: Approx. 227 hp (WRX) Fuel System Fuel Injection: Sequential Electronic Fuel Injection (SFI) Fuel Type: Premium Unleaded (91+ Octane Recommended for STI/Turbo models) Ignition System Ignition Type: Distributorless Ignition System (DIS) with Coil-On-Plug (COP) or Coil-Near-Plug (CNP) depending on specific engine variant. 🔧 Transmission Standard Sti Transmission: 6-speed Manual Transmission Optional Non Sti Transmission Options: 4-speed Automatic Transmission (available on some non-STI models) Features Dccd System: Driver Controlled Center Differential (DCCD) on STI models, allowing manual adjustment of front-to-rear torque split. AWD System: Subaru Symmetrical All-Wheel Drive system with viscous coupling center differential (for non-DCCD models) or electronically controlled center differential (for DCCD models). Fluid Specifications Manual Transmission Fluid: Subaru Extra-S Gear Oil (API GL-5, SAE 75W-90) or equivalent. Rear Differential Fluid: Subaru Extra-S Gear Oil (API GL-5, SAE 75W-90) or equivalent. 📐 Dimensions Exterior Wheelbase: Approx. 100.1 inches (2540 mm) Length: Approx. 173.8 inches (4415 mm) Width: Approx. 68.7 inches (1745 mm) Height: Approx. 56.1 inches (1425 mm) Weights Curb Weight:...

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Tags: 2004 Car Engines H4DOTC Impreza STI Subaru

Product variants

Description

🏷️ Basic Information

Identification

Make:

Subaru

Model:

Impreza

Year:

Trim Level:

WRX STI

Engine Variants Covered:

• STI (EJ207/EJ257)

• H4SO (Naturally Aspirated EJ20/EJ25)

• H4DOTC (Turbocharged EJ20/EJ25)

Codes

Chassis Code:

👋 Introduction

Market Position

Positioning:

The 2004 Subaru Impreza, particularly the WRX STI variant, occupied a prominent position in the enthusiast compact performance car market, known for its rally-inspired engineering, all-wheel-drive capabilities, and potent turbocharged engines.

Competitive Analysis

Competitors:

Competed against vehicles like the Mitsubishi Lancer Evolution, Volkswagen Golf GTI, Honda Civic Si, and Ford Focus SVT, differentiating itself with its standard Symmetrical All-Wheel Drive and boxer engine configuration.

Key Features

Performance Highlights:

Turbocharged Boxer engines, Symmetrical All-Wheel Drive, sport-tuned suspension, advanced driver-controlled center differential (DCCD) on STI models, and a robust chassis.

Manual Value

Utility For Owners:

An indispensable resource for owners seeking to perform maintenance, diagnose issues, or undertake repairs, enabling them to maintain the performance and longevity of their vehicle.

📋 Manual Details

Coverage Areas

Major Systems:

• Engine (STI, Naturally Aspirated, Turbocharged)

• Transmission (Manual, Automatic - though emphasis on Manual for STI)

• Chassis (Suspension, Steering, Brakes, Drivetrain)

• Body (Exterior and Interior)

• Electrical System (Wiring Diagrams, Components, Diagnostics)

Page Count

Estimated Pages:

1000+

Manual Type

Type:

Factory Service Manual / Workshop Repair Manual

Language

Language:

English

Format

Format:

PDF Download

📖 Manual Coverage

Systems Covered

Powertrain:

Detailed coverage of EJ207/EJ257 STI engines (including turbocharger system, fuel injection, ignition, emissions), EJ20/EJ25 naturally aspirated engines, and EJ20/EJ25 turbocharged engines. Comprehensive transmission information for manual transmissions, including clutch, gearbox, differential, and AWD system.

Suspension And Steering:

Front and rear suspension (MacPherson strut front, multi-link rear), steering system (rack and pinion), wheel alignment specifications, shock absorber and spring replacement procedures.

Braking System:

Front and rear disc brakes, ABS system, brake fluid specifications, caliper and rotor replacement, brake bleeding procedures. STI specific Brembo brake system details.

Electrical System:

Complete wiring diagrams for all vehicle systems, ECU pinouts, component locations, diagnostic procedures for electrical faults, lighting, audio system, power accessories, and safety systems.

Body And Interior:

Body panel removal and installation, door mechanisms, interior trim, seat removal, glass replacement, crash structure details.

Procedures Included

Diagnostics And Troubleshooting:

Systematic troubleshooting charts for common issues, DTC (Diagnostic Trouble Code) interpretations, and diagnostic flowcharts for engine, transmission, and electrical systems.

Maintenance:

Routine maintenance tasks such as oil changes, filter replacements, spark plug replacement, coolant flush, brake inspections, and belt inspections.

Repair And Overhaul:

Detailed step-by-step instructions for major component overhauls, including engine rebuilds (pistons, rings, bearings, cylinder heads), transmission rebuilds, clutch replacement, brake system overhauls, and suspension component replacement.

Special Tools And Jigs:

Identification and usage guidelines for specific tools required for Subaru Impreza repairs and maintenance, including specialized engine and transmission tools.

Technical Depth

Depth:

Comprehensive, covering everything from basic maintenance and fluid checks to complete engine and transmission rebuilds, advanced electrical diagnostics, and chassis component overhauls. Suitable for professional technicians and advanced DIY enthusiasts.

📊 Manual Specifications

File Format

File Type:

Searchability:

Searchable text content for quick information retrieval.

Printability:

Printable pages for on-the-job reference.

Print Quality

Image Resolution:

High-resolution diagrams, illustrations, and photographs.

Binding Type

Binding:

N/A (Digital Download)

Paper Type

Paper:

N/A (Digital Download)

⚙️ Engine Specifications

Primary Engine

Sti Engine Code:

EJ257 (North American Market), EJ207 (JDM/European Market)

Sti Engine Type:

Intercooled Turbocharged, Horizontally Opposed (Boxer), DOHC, 16-valve

Sti Displacement:

2.5 Liters (EJ257) / 2.0 Liters (EJ207)

Sti Horsepower:

Approx. 300 hp (STI)

Sti Torque:

Approx. 300 lb-ft (STI)

Naturally Aspirated Engine

Naturally Aspirated Engine Code:

EJ253 (e.g., 2.5 RS)

Naturally Aspirated Engine Type:

Naturally Aspirated, Horizontally Opposed (Boxer), SOHC (some variants), DOHC (some variants), 16-valve

Naturally Aspirated Displacement:

2.5 Liters

Naturally Aspirated Horsepower:

Approx. 165-170 hp

Turbocharged Engine

Turbocharged Engine Code:

EJ255 (e.g., WRX)

Turbocharged Engine Type:

Intercooled Turbocharged, Horizontally Opposed (Boxer), DOHC, 16-valve

Turbocharged Displacement:

2.5 Liters

Turbocharged Horsepower:

Approx. 227 hp (WRX)

Fuel System

Fuel Injection:

Sequential Electronic Fuel Injection (SFI)

Fuel Type:

Premium Unleaded (91+ Octane Recommended for STI/Turbo models)

Ignition System

Ignition Type:

Distributorless Ignition System (DIS) with Coil-On-Plug (COP) or Coil-Near-Plug (CNP) depending on specific engine variant.

🔧 Transmission

Standard

Sti Transmission:

6-speed Manual Transmission

Optional

Non Sti Transmission Options:

4-speed Automatic Transmission (available on some non-STI models)

Features

Dccd System:

Driver Controlled Center Differential (DCCD) on STI models, allowing manual adjustment of front-to-rear torque split.

AWD System:

Subaru Symmetrical All-Wheel Drive system with viscous coupling center differential (for non-DCCD models) or electronically controlled center differential (for DCCD models).

Fluid Specifications

Manual Transmission Fluid:

Subaru Extra-S Gear Oil (API GL-5, SAE 75W-90) or equivalent.

Rear Differential Fluid:

Subaru Extra-S Gear Oil (API GL-5, SAE 75W-90) or equivalent.

📐 Dimensions

Exterior

Wheelbase:

Approx. 100.1 inches (2540 mm)

Length:

Approx. 173.8 inches (4415 mm)

Width:

Approx. 68.7 inches (1745 mm)

Height:

Approx. 56.1 inches (1425 mm)

Weights

Curb Weight:

Approx. 3100-3300 lbs (STI, depending on options)

Gross Vehicle Weight Rating:

Varies by model, consult specific VIN

Wheels And Tires

Wheel Size:

17x7.5 or 17x8.0 (STI); 16-inch or 17-inch (other models)

Tire Size:

225/45R17 (STI); 205/55R16 or 215/45R17 (other models)

Bolt Pattern:

5x100mm

🛡️ Safety Features

Ratings

NHTSA Front Impact:

4 Stars (Driver), 4 Stars (Passenger)

NHTSA Side Impact:

5 Stars (Driver), 5 Stars (Passenger)

IIHS Moderate Overlap Front:

Active Features

Standard Anti-lock Braking System (ABS)

Traction Control:

Traction Control System (TCS) available on some models.

Stability Control:

Electronic Stability Control (ESC) not widely available on 2004 Impreza models.

Passive Features

Airbags:

Front driver and passenger airbags, side curtain airbags (optional on some models).

Seatbelts:

Three-point height-adjustable front seatbelts with pretensioners and load limiters, three-point rear seatbelts.

💡 Technology Features

Infotainment

Audio System:

Factory-installed CD player, AM/FM radio. Higher trims may offer premium audio systems (e.g., McIntosh in some STI variants).

Navigation:

Factory navigation systems were not widely available or standard on most 2004 Impreza models.

Driver Assistance

Cruise Control:

Standard on most models.

Connectivity

Auxiliary Input:

Not typically standard; aftermarket solutions are common for modern audio connectivity.

🔧 Maintenance

Service Intervals

Oil Change Interval:

Every 3,750 miles (severe duty) or 7,500 miles (normal duty), or 6 months/12 months respectively. Consult manual for specifics.

Engine Air Filter:

Replace every 15,000 miles or as needed based on conditions.

Spark Plugs:

Replace approximately every 60,000 miles (refer to manual for exact type and interval).

Timing Belt:

Not applicable for these EJ-series engines; they utilize a timing chain or timing belt with tensioners and idlers that require replacement based on mileage/age (typically 105,000 miles).

Fluid Specifications

Engine Oil Type:

API SN/SP, ILSAC GF-6A compatible, SAE 0W-20 or 5W-30 (check manual for specific recommendations based on engine variant and climate).

Coolant Type:

Subaru Super Coolant (Blue) or equivalent silicate-free, long-life coolant.

Brake Fluid Type:

DOT 3 or DOT 4 brake fluid.

Known Issues

Engine Oil Consumption:

Some EJ25 engines (particularly the EJ255 and EJ257) are known for potentially higher oil consumption. Regular oil level checks are crucial.

Head Gaskets:

While less common in the EJ257 than earlier Subaru engines, head gasket leaks can still occur and are a critical repair. The manual details inspection and replacement procedures.

Clutch Wear:

Due to the performance nature of the STI, clutch wear can be accelerated with aggressive driving. The manual provides clutch inspection and replacement steps.

Turbocharger Issues:

Turbocharger seals, wastegate actuation, and intercooler efficiency are critical points for turbocharged models. The manual covers troubleshooting and maintenance for these components.

📚 Vehicle History

Brand Heritage

Subaru Heritage:

Subaru, the automotive division of Subaru Corporation, has a long history in aviation and a strong reputation for its horizontally opposed boxer engines and Symmetrical All-Wheel Drive systems, particularly in rally racing.

Model Evolution

Impreza Generation:

The 2004 Impreza represents the second generation (GD/GG chassis) of the Impreza, introduced in 2000. This generation saw significant design and engineering updates, with the WRX and WRX STI variants gaining widespread international acclaim.

2004 Updates:

The 2004 model year included a significant facelift, often referred to as the 'Bugeye' to 'Blobeye' transition, featuring new headlights, grille, front bumper, and updated interior styling for most models. The STI model received further performance enhancements.

Production

Manufacturing Location:

Primarily manufactured in Japan.

🏆 Awards & Recognition

Recognitions

Performance Awards:

The Subaru Impreza WRX and WRX STI have consistently received accolades in performance and enthusiast publications for their driving dynamics, handling, and all-wheel-drive performance, often cited for their 'rally car for the road' pedigree.

Ratings

Car And Driver Ranking:

The WRX STI variant was frequently included in '10Best' lists and praised for its accessible performance and handling characteristics.