The 2004 WRX STI with its EJ257 is a high-strung performance machine that demands respect and maintenance. When modified or abused, catastrophic engine failure is common; when maintained properly, the drivetrain proves surprisingly durable, but several signature issues still plague even well-kept examples.
Head Gasket Failure (External Leaks)
Common · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: Oil seepage around cylinder heads visible on block exterior, Coolant weeping from head mating surface, Slight oil smell after hard driving, No overheating or mixing of fluids initially
Fix: Multi-layer steel (MLS) gasket replacement with proper machine work. Requires pulling engine or extensive disassembly. 12-16 labor hours depending on shop approach. Critical to resurface heads flat and check for warpage. OEM gaskets last longer than aftermarket on stock boost.
Estimated cost: $2,000-3,500
Ringland Failure / Piston #4 Failure
Occasional · high severity
Typical onset: 50,000-120,000 mi
Symptoms: Sudden loss of compression in cylinder 4, Heavy misfires under boost, White/blue smoke on startup or under load, Metallic rattling from engine, CEL with P0304 misfire code
Fix: Complete engine rebuild or short block replacement. Piston #4 runs leanest due to unequal-length headers. Catastrophic on modified cars running aggressive tunes or poor-quality fuel. Forged pistons recommended on rebuild. 20-30 labor hours for removal, rebuild, reinstall.
Estimated cost: $4,500-8,000
Turbocharger Failure (IHI VF39)
Occasional · medium severity
Typical onset: 80,000-130,000 mi
Symptoms: Excessive oil consumption (burning oil), Blue smoke from exhaust under boost, Whining or whistling noise on acceleration, Loss of boost pressure, Oil in intercooler piping
Fix: Turbo seal failure or shaft play requires replacement or rebuild. OEM turbos are expensive; quality aftermarket options exist. 6-8 labor hours for R&R including oil/coolant lines, downpipe, intake. Always replace oil feed/return lines and check banjo bolt filters.
Estimated cost: $1,800-3,200
Transmission Synchro Wear (2nd Gear)
Common · low severity
Typical onset: 70,000-110,000 mi
Symptoms: Grinding into 2nd gear when cold, Difficult engagement of 2nd under aggressive shifting, Crunching noise on 1-2 or 2-3 shifts, Worse with heavy clutch use or high-RPM shifts
Fix: Six-speed synchros wear from hard use and clutch dumping. Full transmission rebuild with new synchro assemblies. 8-12 labor hours for removal, rebuild, reinstall. Some shops offer upgraded brass synchros. Can limp along if shifted gently, but eventual rebuild needed.
Estimated cost: $2,500-4,000
Engine Knock/Detonation from Improper Modifications
Common · high severity
Symptoms: Audible pinging or rattling under boost, Engine surging or hesitation, Loss of power, CEL with knock sensor codes, Engine damage progressing rapidly if ignored
Fix: Not a failure, but a deadly mistake on these cars. Aftermarket intakes, exhausts, or boost controllers without proper ECU tuning cause catastrophic detonation. Requires professional dyno tune (3-5 hours) or return to stock. Once knock damage occurs, full engine rebuild required. Prevention is everything.
Estimated cost: $800-1,200 (tune) or $5,000-9,000 (rebuild after damage)
Timing Belt and Water Pump
Common · high severity
Typical onset: 60,000-105,000 mi
Symptoms: None until failure, Sudden engine death if belt breaks, Coolant leak from water pump, Squealing from belt area
Fix: Interference engine — belt failure destroys valves and pistons. 105k mile interval per Subaru, but many techs recommend 60k on performance-driven cars. Always replace water pump, tensioner, and idlers together. 5-7 labor hours. Non-negotiable maintenance.
Estimated cost: $800-1,400
Rear Differential Fluid Breakdown
Occasional · medium severity
Typical onset: 40,000-80,000 mi
Symptoms: Whining from rear end on deceleration, Clunking during direction changes, Vibration under acceleration, Burnt fluid smell, Metal shavings in differential fluid
Fix: R180 rear diff takes abuse from AWD launches and limited-slip operation. Fluid breaks down faster than manual interval suggests. Drain/fill every 30k miles prevents failure. Damaged diffs need R&R and rebuild. 3-4 hours for fluid change, 8-12 for rebuild.
Estimated cost: $150-250 (fluid) or $1,200-2,000 (rebuild)
Owner tips
Change engine oil every 3,000 miles with quality synthetic — these engines are oil-sensitive, especially with high boost.
Never modify intake, exhaust, or boost without a professional tune from a Subaru specialist.
Replace transmission and differential fluids every 30,000 miles, not Subaru's extended intervals.
Use 93+ octane fuel exclusively; lower grades invite detonation and engine damage.
Timing belt at 60,000 miles, not 105,000 — interference engine failure is catastrophic.
Pre-purchase compression and leakdown tests are mandatory; these engines hide damage until sudden failure.
Buy only with complete service records and proof of timing belt service; avoid heavily modified examples unless you can afford a $6k engine rebuild as a surprise.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 23V076000
2023-02-13
Subaru of America, Inc. (Subaru) is recalling certain 2004-2005 Impreza and WRX vehicles that received replacement front passenger air bag inflators under a previous recall. The replacement air bag inflators may have been installed incorrectly.
Consequence: An incorrectly installed inflator may not properly inflate the passenger air bag, increasing the risk of injury during a crash.
Remedy: Dealers will inspect the passenger inflator and if necessary, install a new inflator kit, free of charge. Owner notification letters are expected to be mailed April 14, 2023. Owners may contact Subaru's customer service at 1-844-373-6614. Subaru's number for this recall is WRF-23.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 20V001000
2020-01-02 · EA15001
Subaru of America, Inc. (Subaru) is recalling certain 2009-2013 Forester, 2003-2006 Baja, 2004-2011 Impreza, 2004-2014 WRX (STI included), 2003-2014 Legacy and Outback, and 2005-2006 Saab 9-2X vehicles originally sold, or ever registered, in the states of Alabama, California, Florida, Georgia, Hawaii, Louisiana, Mississippi, South Carolina, Texas, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands (Saipan), and the U.S. Virgin Islands or "Zone A."
These vehicles had their passenger frontal air bag inflators previously replaced under a prior recall using inflators of the same design. The inflators may explode due to propellant degradation occurring after long-term exposure to high absolute humidity, temperature and temperature cycling.
Consequence: An inflator explosion may result in sharp metal fragments striking the driver or other occupants resulting in serious injury or death.
Remedy: Subaru will notify their owners. General Motors will notify Saab owners. Dealers will replace the passenger air bag inflators with alternate inflators, free of charge. The recall began January 7, 2020. Subaru Owners may contact Subaru customer service at 1-844-373-6614. Saab owners may contact the Saab Customer Assistance Center at 1-800-955-9007. Subaru's number for this recall is TKA-20.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 20V002000
2020-01-02 · EA15001
Subaru of America, Inc. (Subaru) is recalling certain 2009-2013 Forester, 2003-2006 Baja, 2004-2011 Impreza, 2004-2014 WRX (including STI), 2003-2014 Legacy and Outback, and 2006 Saab 9-2X vehicles originally sold, or ever registered, in the states of Arizona, Arkansas, Delaware, District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Missouri, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, and West Virginia or "Zone B."
These vehicles had their passenger frontal air bag inflators previously replaced under a prior recall using inflators of the same design. The inflators may explode due to propellant degradation occurring after long-term exposure to high absolute humidity, temperature and temperature cycling.
Consequence: An inflator explosion may result in sharp metal fragments striking the driver or other occupants resulting in serious injury or death.
Remedy: Subaru will notify their owners. General Motors will notify Saab owners. Dealers will replace the passenger air bag inflators, free of charge. The recall began January 7, 2020. Subaru owners may contact Subaru customer service at 1-844-373-6614. Saab owners may contact the Saab Customer Assistance Center at 1-800-955-9007. Subaru's number for this recall is TKB-20.
AIR BAGS:FRONTAL:PASSENGER SIDE:INFLATOR MODULE · 20V003000
2020-01-02 · EA15001
Subaru of America, Inc. (Subaru) is recalling certain 2009-2013 Forester, 2003-2006 Baja, 2004-2011 Impreza, 2004-2014 WRX (including STI), 2003-2014 Legacy and Outback, and 2005-2006 Saab 9-2X vehicles originally sold, or ever registered, in the states of Alaska, Colorado, Connecticut, Idaho, Iowa, Maine, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New York, North Dakota, Oregon, Rhode Island, South Dakota, Utah, Vermont, Washington, Wisconsin, and Wyoming or "Zone C."
These vehicles had their passenger frontal air bag inflators previously replaced under a prior recall using inflators of the same design. The inflators may explode due to propellant degradation occurring after long-term exposure to high absolute humidity, temperature and temperature cycling.
Consequence: An inflator explosion may result in sharp metal fragments striking the driver or other occupants resulting in serious injury or death.
Remedy: Subaru will notify their owners. General Motors will notify Saab owners. Dealers will replace the passenger air bag inflators, free of charge. The recall began January 7, 2020. Subaru owners may contact Subaru customer service at 1-844-373-6614. Saab owners may contact the Saab Customer Assistance Center at 1-800-955-9007. Subaru's number for this recall is TKC-20.
EXTERIOR LIGHTING · 06E060000
2006-06-29
CERTAIN AAI MOTORSPORTS COMBINATION LAMPS SOLD AS REPLACEMENT LAMPS FOR USE ON THE ABOVE LIST PASSENGER VEHICLES. COMBINATION LAMPS NOT EQUIPPED WITH AMBER SIDE REFLECTORS FAIL TO CONFORM WITH THE REQUIREMENTS OF FEDERAL MOTOR VEHICLE SAFETY STANDARD NO. 108, "LAMPS, REFLECTIVE DEVICES, AND ASSOCIATED EQUIPMENT."
Consequence: LACK OF AMBER SIDE REFLECTORS IN THE LAMPS WILL DECREASE LIGHTING VISIBILITY TO OTHER DRIVERS AND MAY POSSIBLY RESULT IN A VEHICLE CRASH
Remedy: AAI MOTORSPORTS WILL NOTIFY OWNERS AND REPLACE THE LAMPS FREE OF CHARGE. THE RECALL BEGAN ON AUGUST 1, 2006. OWNERS MAY CONTACT AAI MOTORSPORTS AT 909-923-9188.
Vehicle Info — 2004 Subaru WRX STI
Performance
Horsepower
300hp
Torque
300lb-ft
0–60 mph
4.9sec
Quarter mile
13.5sec
Top speed
155mph
Capability & size
Curb weight
3,263lb
Wiper blades
GD chassis, first year in US market. Sedan body style has no rear wiper.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2004 Subaru WRX STI 2.5L H4 Turbo EJ257 and can vary by trim.
🔧 Built by master technician Chris Hackleman · Master Technician · 20+ years.