🏷️ Basic Information

Make:

Subaru

Model:

Impreza

Year:

2004

Engine Variant:

2.5L (gasoline)

Chassis Code:

GDA/GDB (WRX/STI variants), GGA (Wagon)

Engine Code:

EJ253 (Naturally Aspirated), EJ255/EJ257 (Turbocharged)

👋 Introduction

Segment:

Compact/Subcompact Sedan and Wagon, known for its sporty handling and All-Wheel Drive (AWD) capability.

Target Audience:

Enthusiast drivers, DIY mechanics, and owners seeking comprehensive repair and maintenance information.

Key Competitors:

Honda Civic, Toyota Corolla, Mazda3, Mitsubishi Lancer.

Unique Selling Proposition:

Standard Symmetrical All-Wheel Drive (on most models), Subaru's boxer engine configuration, rally-inspired WRX and STI variants.

Powertrain Options:

Naturally aspirated 2.5L boxer engine and turbocharged 2.0L/2.5L boxer engines (WRX/STI).

Drivetrain:

Symmetrical All-Wheel Drive (standard on most trims).

📋 Manual Details

Primary Coverage:

2004 Subaru Impreza 2.5L (gasoline)

Trim Level Coverage:

All trim levels including RS, Outback Sport, WRX (turbocharged 2.0L/2.5L) and potentially STI (2.5L turbocharged) depending on specific manual variations.

Estimated Page Count:

Over 2000 pages (typical for a comprehensive factory service manual)

Type:

Factory Service Repair Manual

Language:

English

Format:

Digital (PDF), potentially printable sections

📖 Manual Coverage

Engine Management:

ECU diagnosis, sensor inputs/outputs, fuel control, ignition timing, emission control systems (EVAP, EGR), drive-by-wire throttle control (if applicable to specific trims).

Engine Mechanical:

Engine assembly/disassembly, cylinder head, block, crankshaft, pistons, connecting rods, valve train, timing belt/chain, oil pump, cooling system, lubrication system.

Fuel System:

Fuel pump, fuel filter, fuel injectors, fuel lines, fuel pressure regulator, fuel tank, EVAP system.

Transmission Manual:

Clutch system, gearshift linkage, transmission disassembly/assembly, gear ratios, shift forks, synchronizers, bearings.

Transmission Automatic:

Torque converter, transmission fluid control, valve body, planetary gear sets, clutches, bands, electronic controls, shift solenoids.

Drivetrain:

Front and rear differentials, transfer case (AWD systems), driveshafts, CV joints, wheel bearings.

Suspension:

Front MacPherson struts, rear multi-link suspension, control arms, sway bars, bushings, springs, shock absorbers.

Steering:

Power steering system (hydraulic/electric), steering rack, tie rods, steering column, wheel alignment specifications.

Brakes:

Front and rear brake systems (disc/drum), ABS system, brake fluid, master cylinder, calipers, rotors, brake lines, parking brake.

Electrical System:

Battery, alternator, starter motor, wiring diagrams, fuses, relays, lighting system, horn, ignition system.

HVAC:

Air conditioning system (compressor, condenser, evaporator, refrigerant), heater core, blower motor, climate control system.

Body And Interior:

Body panels, doors, hood, trunk, windows, seats, dashboard, trim components, body sealing.

Safety Systems:

Airbag system, seatbelt pretensioners, SRS warning lights and diagnosis.

Routine Maintenance:

Oil changes, filter replacements, fluid checks and changes, spark plug replacement, air filter replacement.

Engine Repair:

Complete engine overhaul, cylinder head gasket replacement, piston ring replacement, bearing replacement, timing belt replacement.

Transmission Service:

Clutch replacement, transmission fluid flush and replacement, internal transmission repairs.

Brake Service:

Brake pad and rotor replacement, caliper servicing, brake bleeding, ABS component replacement.

Suspension And Steering Repair:

Ball joint replacement, tie rod end replacement, control arm bushing replacement, strut and shock absorber replacement, power steering pump replacement.

Electrical Diagnostics:

Troubleshooting electrical faults using wiring diagrams, component testing, diagnostic trouble codes (DTCs).

HVAC Repair:

Refrigerant recharge, compressor replacement, blower motor replacement, leak detection.

Bodywork And Trim:

Panel replacement, door alignment, interior trim removal and installation.

Troubleshooting:

Systematic diagnostic procedures for common and uncommon vehicle issues.

Diagnostic Capability:

Advanced diagnostic procedures, including component testing, circuit analysis, and use of diagnostic scan tools.

Repair Scope:

Covers everything from basic maintenance to complete engine and transmission rebuilds, including specialized procedures for AWD systems and turbocharged engines.

Specification Detail:

Provides precise torque specifications, clearances, fluid capacities, and electrical resistance values for all major components.

📊 Manual Specifications

Digital Format:

PDF (Portable Document Format)

Diagram Clarity:

High-quality, clear diagrams and illustrations.

Text Readability:

Easy-to-read text sections, optimized for digital viewing and printing.

Digital Access:

Downloadable file, accessible on computers, tablets, and smartphones.

Digital Nature:

N/A (Digital Format)

⚙️ Engine Specifications

Engine Type:

Naturally Aspirated Boxer-4 Cylinder (EJ253)

Displacement:

2.5 Liters (2457 cc)

Bore X Stroke:

99.5 mm x 79.0 mm

Compression Ratio:

9.7:1

Valve Train:

DOHC, 16 Valves

Horsepower Na:

Approximately 165-175 hp @ 5600-5800 rpm (varies slightly by specific model/trim)

Torque Na:

Approximately 166-170 lb-ft @ 4000 rpm (varies slightly by specific model/trim)

Horsepower Turbo:

WRX: Approx. 227-230 hp @ 5600 rpm; STI: Approx. 300 hp @ 6000 rpm

Torque Turbo:

WRX: Approx. 235-237 lb-ft @ 3600-4000 rpm; STI: Approx. 300 lb-ft @ 4000 rpm

Fuel Delivery:

Electronic Fuel Injection (EFI)

Fuel Type:

Unleaded gasoline (87 octane recommended for NA, 91+ octane for WRX/STI)

Ignition System:

Distributorless Ignition System (DIS) with coil-on-plug

🔧 Transmission

Transmission Type:

5-speed Manual (all models)

Transmission Type:

4-speed Automatic (available on non-WRX models)

AWD Integration:

Symmetrical All-Wheel Drive with viscous coupling center differential (manual) or electronically controlled AWD (automatic).

Sti Transmission:

6-speed manual transmission with DCCD (Driver Controlled Center Differential) on STI models.

📐 Dimensions

Length:

Approx. 179.7 inches (Sedan), 177.0 inches (Wagon)

Width:

Approx. 68.7 inches

Height:

Approx. 56.1 inches (Sedan), 58.7 inches (Wagon)

Wheelbase:

Approx. 104.3 inches

Curb Weight:

Approx. 2900-3100 lbs (varies by trim and transmission)

🛡️ Safety Features

NHTSA Frontal Crash:

5-Star (driver and passenger)

IIHS Frontal Offset:

Good

ABS:

Standard Anti-lock Braking System (ABS)

AWD:

Standard Symmetrical All-Wheel Drive for enhanced traction and stability.

Airbags:

Driver and front passenger airbags, side curtain airbags (optional on some trims).

Seatbelts:

3-point height-adjustable front seatbelts with pretensioners and load limiters.

💡 Technology Features

Audio System:

Factory AM/FM/CD player with 4-6 speakers. Optional premium audio systems may be available. Auxiliary input often absent or proprietary.

Traction Control:

Traction Control System (TCS) and Vehicle Dynamics Control (VDC) available on some trims/optional.

Cruise Control:

Standard cruise control.

🔧 Maintenance

Oil Change Interval:

Every 3,750 miles or 3.75 months (severe conditions) or 7,500 miles or 7.5 months (normal conditions), consult specific manual for exact intervals.

Timing Belt Replacement:

Typically every 105,000 miles or 7 years for turbocharged engines (EJ205/EJ255/EJ257). Naturally aspirated EJ253 may use a timing chain or belt depending on specific build codes, consult manual. High-risk component for failure if not replaced.

Spark Plug Replacement:

Approximately 60,000 miles (NGK Iridium or Platinum recommended).

Engine Oil:

SAE 5W-30 (API SG or higher). For turbocharged engines, 5W-30 or 10W-30 Synthetic often recommended. Check manual for specific viscosity based on temperature.

Coolant:

Subaru Genuine Coolant (Blue) or equivalent phosphate-free OAT coolant. Mixture of 50/50 with distilled water.

Transmission Fluid Manual:

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

Transmission Fluid Automatic:

Subaru ATF-HP (High Performance) or equivalent Dexron III/Mercon compatible fluid.

Brake Fluid:

DOT 3 or DOT 4 brake fluid.

Head Gaskets:

While less common than on earlier EJ25 engines, head gasket leaks can still occur, especially with age and heat cycling. Look for coolant loss, milky oil, or exhaust gases in coolant.

Turbocharger Issues:

WRX/STI models can experience turbo wear, especially if oil maintenance is neglected or boost levels are excessively high. Check for oil leaks, blue smoke from exhaust, or reduced power.

Clutch Wear:

Manual transmission clutches can wear out with aggressive driving or high mileage. Symptoms include slipping, difficulty shifting, or clutch pedal issues.

Suspension Bushings:

Rubber suspension bushings can degrade over time, leading to clunks, poor handling, and premature tire wear.

Catalytic Converter:

Early failure or clogging of the catalytic converter can occur, leading to reduced engine performance and check engine lights.

📚 Vehicle History

Subaru Legacy:

Subaru, founded in 1953, is renowned for its pioneering use of the boxer engine and Symmetrical All-Wheel Drive system, often associated with ruggedness and performance, particularly in rally racing.

Gc Gd Generation:

The 2004 Impreza belongs to the second generation (GD/GG chassis, 2000-2007), which saw significant styling changes, improved chassis rigidity, and the introduction of more powerful WRX and STI variants.

Manufacturing Location:

Japan (Gunma Prefecture)

🏆 Awards & Recognition

Car And Driver:

Subaru Impreza WRX models frequently appeared on Car and Driver's 10Best lists during this era for their performance and value.

Rally Heritage:

The Impreza platform has a strong heritage in motorsports, particularly in the World Rally Championship (WRC), contributing to its performance image.