Parts for your 2005 Subaru Impreza-Ignition coils

2005 Subaru Impreza ignition coils: purpose, care, and when to replace

Referencing technical sources: the Subaru Factory Service Manual for MY2005 Impreza and Subaru’s FAST/STIS parts catalogues specify ignition coils for all 2005 petrol Impreza variants. WRX (EJ20 turbo) models use four individual coil-on-plug units, while naturally aspirated 2.5 models use a twin-outlet coil pack feeding spark plug leads. So ignition coils are definitely fitted and relevant on the 2005 Subaru Impreza.

The ignition coil’s job is simple but critical: it transforms the car’s 12-volt supply into the tens of thousands of volts needed to jump the spark plug gap. On a 2005 Impreza WRX each cylinder has its own coil-on-plug, tucked under the cam covers. On many non-turbo 2.5 models there’s a single coil pack with two internal coils sending spark to four plugs via leads. Either way, healthy coils are key to crisp starts, smooth idle and clean power.

Coils don’t have a fixed replacement interval in Subaru servicing, they’re replaced on condition. Telltale signs include:

• Misfire under load, rough idle, hesitation or flat spots
• Worse fuel economy and a sulphur smell from the exhaust
• Check Engine Light with codes like P0301–P0304 (misfire) or P0351–P0354 (coil circuit)

Good practice during routine servicing helps coils live longer. Keep moisture out of connectors, inspect boots and plug leads for cracking or carbon tracking, and use a dab of dielectric grease on boots when refitting. If one WRX coil fails, many owners replace just the faulty unit, but on higher‑kilometre cars it's sensible to test all four and consider a matched pair or set. On coil-pack cars, failing plug leads are common culprits, swap the full lead set if resistance or insulation is suspect.

When replacing, stick with quality OEM or reputable aftermarket coils. Fit the correct spark plugs, set the gap to spec, and avoid yanking on leads—use the boot. For COP bolts, use a small torque wrench and follow the Subaru spec in the service manual to avoid cracking housings. After installation, clear any codes and road test under load to confirm the fix.

DIYers will want a 10 mm socket, extensions, and patience around the tight WRX engine bay. If the car is stumbling badly, don’t keep driving, raw fuel can damage the catalytic converter (and on turbos, the oxygen sensors and turbocharger as well).

How many ignition coils does a 2005 Subaru Impreza have?

WRX models run four individual coil-on-plug units—one per cylinder. Most non-turbo 2.5 models use a single twin-coil pack that fires pairs of cylinders via four spark plug leads.

What fault codes point to a bad coil on a 2005 Impreza?

Common codes include P0301–P0304 for cylinder-specific misfires and P0351–P0354 for ignition coil primary/secondary circuit faults. Always check plugs and leads before condemning a coil, especially on coil-pack cars.

Is it safe to drive with a failing ignition coil?

Not recommended. Misfires can overheat and poison the catalytic converter and, on turbo models, can stress the turbo and sensors. It’s best to diagnose and repair promptly to avoid bigger bills.