2004 Subaru Impreza Headlight Guide: Halogen vs. STi HID and Common Failures

Understanding the 'Blobeye' Headlights: Halogen vs. HID

The 2004 Subaru Impreza, part of the 'Blobeye' generation (2004-2005), was offered with two distinctly different types of headlamp assemblies. Understanding which version your car has is the most important step in diagnosing issues or buying a replacement.

Halogen Headlights (Impreza 2.5RS, Outback Sport, WRX)

The standard Impreza models and the WRX came from the factory with halogen headlights. These use a reflector-style housing with a halogen bulb (size H1 for the low beam) that contains a heated tungsten filament to produce a yellowish-white light. They are simple, reliable, and less expensive to replace.

HID/Xenon Headlights (WRX STi Only)

The high-performance WRX STi model came exclusively with High-Intensity Discharge (HID), also known as Xenon, headlights. These use a projector-style housing for a more focused beam. Instead of a filament, HID systems use an electrical arc between two electrodes to ignite xenon gas inside the bulb (size D2S), producing a brighter, whiter light. These systems require an external ballast and igniter to create and maintain the high voltage needed to operate.

Visual Differences: Chrome vs. Black Chrome Housings

Beyond the lighting technology, there were cosmetic differences. The 2004 WRX STi came with a traditional chrome internal housing. For the 2005 model year, Subaru switched to a darker, 'black chrome' or smoked housing for the STi. Some WRX owners also opted for aftermarket or JDM-style black housing lights. When replacing a single headlight, it is crucial to match the housing color of your remaining light to ensure a consistent appearance.

Symptoms of a Failing Headlamp Assembly

• Dim or Flickering Light: While often a sign of a failing bulb, flickering can also point to a bad connection in the wiring harness or a failing ballast on HID models.
• Moisture or Condensation Inside: Water droplets or a persistent fog inside the lens indicates the seal between the lens and the housing has failed. This can short out bulbs and corrode reflective surfaces.
• Yellowed or Hazy Lens: The outer polycarbonate lens can become cloudy and yellow from UV sun damage over time. This significantly reduces light output and can be a safety hazard.
• Melted Connectors: Previous owners may have used high-wattage aftermarket bulbs that generate too much heat, melting the plastic connector on the back of the assembly.
• Intermittent or Dead Headlight: If a new bulb and fuse don't solve the problem, the issue could be within the assembly's internal wiring or the main vehicle-side connector.

Known Issues, Recalls, and TSBs for 2004 Impreza Headlights

Common Owner-Reported Issues

The most common complaint for headlights of this era is seal failure leading to condensation. Over time, the factory sealant dries out and cracks, allowing moisture to enter during rain or car washes. Another frequent issue stems from improper modifications by previous owners, such as poorly spliced wires for aftermarket lighting, which can cause a host of electrical problems.

Official Recalls and Technical Service Bulletins (TSBs)

As of mid-2024, there are no active recalls or major TSBs specifically for the headlamp assemblies on the 2004 Subaru Impreza. While there are several prominent airbag recalls for this model year, the lighting system has not been subject to a large-scale factory recall. Any issues like condensation or hazing are generally considered age-related wear and tear.

Buying a Used 2004 Impreza Headlamp: What to Inspect

A used OEM (Original Equipment Manufacturer) headlamp is often a better choice than a cheap aftermarket alternative, as OEM units typically have better optics, beam patterns, and durability. Here’s what to look for:

1. Verify the Type: First, confirm you are buying the correct type: Halogen (for RS/WRX) or HID (for STi). An HID housing will have a circular projector lens visible from the front, while a halogen housing has an open reflector bowl.
2. Check the Housing Color: Look at the internal trim. Is it standard chrome or the darker black chrome? Hold it next to your existing light if possible to ensure a perfect match.
3. Inspect the Lens Condition: Look for deep scratches, rock chips, and internal 'crazing' (a network of fine cracks). Light external hazing or yellowing can often be polished out with a restoration kit, but heavy oxidation or internal damage means the light should be avoided.
4. Examine the Seal: Carefully check the seam where the clear lens meets the black plastic housing. Look for any signs that it has been pried open, or for gaps in the sealant. This is where leaks and condensation start.
5. Check All Mounting Tabs: This is critical. The plastic mounting tabs are brittle and often break during removal or in minor impacts. Ensure all tabs are present and free of cracks. A light with a broken tab will vibrate and can never be aimed correctly.
6. Inspect the Wiring and Connectors: Look at the main electrical connector on the back. Check for any green or white corrosion on the pins, melted plastic, or signs of amateur splicing with electrical tape.
7. Confirm What's Included: Ask if the assembly includes bulbs, rubber dust covers, and the HID ballast (if applicable). These components can be expensive to purchase separately.

Replacement and Aiming Guide

Step-by-Step Replacement

Replacing the headlamp assembly is a straightforward DIY job that typically takes less than an hour per side.

1. Access the Bolts: Open the hood. You will need to remove the front grille to access the headlight bolts. The grille is held on by several plastic clips that can be popped up with a flathead screwdriver.
2. Remove Mounting Bolts: The headlamp is typically secured by two 10mm bolts on the top and one on the side, accessible after the grille is removed.
3. Disconnect Wiring: Carefully pull the assembly forward and disconnect the main electrical harness from the back.
4. Install New Assembly: Connect the new assembly, slide it into place, and reinstall the mounting bolts. Do not overtighten them. Reinstall the grille.

Post-Installation Headlight Aiming

Aiming your new headlights is a mandatory final step for safety. Improperly aimed lights can blind oncoming drivers or fail to illuminate the road properly.

• Park your car on a level surface, 25 feet away from a flat wall or garage door.
• Turn on your low beams.
• On the back of the headlamp assembly, you will find adjustment screws or 8mm bolts. One controls vertical (up/down) aim, and the other controls horizontal (left/right) aim.
• The top of the low beam cutoff line on the wall should be slightly below the height of the center of your headlight lens from the ground. Turn the vertical adjuster to raise or lower the beam into the correct position.

Cost Comparison

Prices for a single 2004 Impreza headlamp assembly can vary significantly based on type and condition.

Frequently Asked Questions (FAQ)