2015–2021 Subaru WRX
By Tom Becker ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
Save $335 by doing it yourself! Shop cost: $450
Quick answer: Spark Plug Replacement on a 2015–2021 Subaru WRX is rated Advanced and takes about 1.5–2 hours. You'll need 7 tools for this job, and parts cost about $115. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Correct spark plug set for 2015-2021 Subaru WRX; verify engine, heat range, gap, and VIN fitment | — | $115.00 | |
| Coil-boot seals or ignition coils only if inspection finds damage Optional | — | $35.00 |
About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.
💡 Pro tip: Order all parts at once to save on shipping
Follow these steps carefully
The WRX’s 2.0L FA20DIT is a turbocharged boxer — the four plugs stick out of the sides of the cylinder heads, two per side, sandwiched between the heads and the frame rails with almost no room to spare.
Unclip the airbox, loosen the intake hose clamp, unplug the mass airflow sensor, and lift the whole assembly out. With it gone you can finally see the two coils hiding down by the frame rail. Disconnect each coil’s electrical connector.
The driver side (LH) is worse. Pull the battery hold-down, remove the cables (negative first), lift the battery and tray out, then unbolt the secondary air pump and move it aside.
Unbolt each coil pack and note the factory trick: the #3 and #4 coils have to be turned 180 degrees to clear the frame rail on the way out. Twist and wiggle them free rather than prying.
Lower a 14mm spark plug socket down the well — the FA20’s OE-spec plugs (NGK ILKAR8H6 type) use a 14mm hex, smaller than the old 5/8-inch standard.
Do not invent a number here. Check the gap spec in your owner’s manual or on the emissions sticker under the hood and verify each new plug with a feeler gauge, adjusting only the ground strap. The FA20DIT runs fine-wire iridium plugs from the factory, and the center electrode is fragile — no prying on it. Thread each plug in by hand until the washer seats; on a boxer you can’t see the threads, so feel for smooth engagement and back off at the first sign of binding. Seat the washer, then about a quarter to half turn more with the ratchet.
Double-check every connector before closing the hood. Start the engine, let it idle, and take it for a drive — then re-scan or listen for the smooth, even idle that says all four cylinders are firing clean.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
2015–2021
2015–2021
2015–2021
2015–2021
2015–2021
2015–2021
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