2017–2023 Subaru Impreza
By Ray Delgado ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
Save $212 by doing it yourself! Shop cost: $260
Quick answer: Spark Plug Replacement on a 2017–2023 Subaru Impreza is rated Advanced and takes about 60-90 minutes. You'll need 5 tools for this job, and parts cost about $48. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Iridium spark plugs for Subaru Impreza (verify engine and heat range) | — | $48.00 | |
| Spark plug boot grease (small tube, optional) Optional | — | $8.00 |
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
You need four. These are ~100,000-mile plugs, but the boxer layout makes this the most access-challenged four-cylinder plug job you'll do: the plugs point sideways out of the cylinder heads, buried between the engine and the frame rails. Scan for misfire codes (P0300-P0304) before ordering.
Disconnect the negative battery cable. Because the plugs are M12-thread, you need a thin-wall 14 mm spark plug socket — verify it against a new plug — plus short extensions and a universal joint.
Because the plugs are M12-thread, you need a thin-wall 14 mm spark plug socket — verify it against a new plug — plus short extensions and a universal joint. I've seen what happens when people ignore that.
Work one side at a time. Squeeze each coil connector's locking tab and pull it straight back, then remove the coil bolt and wiggle each coil straight out of its tube — keep them in order.
Verify the 1.0-1.1 mm gap without prying on the fine iridium electrode. Start each new plug BY HAND for several turns — cross-threading a sideways hole you can't see is the classic boxer disaster — then tighten to the manufacturer's spec in your owner's manual.
I learned this the hard way: Crack each old plug loose with the thin-wall 14 mm socket and extensions, working around the frame rail — patience beats force here.
Press each coil firmly onto its plug until it seats, refit the coil bolts, and reconnect every connector until the tabs click. Reinstall the battery, tray, and air intake duct exactly as they came off — a loose intake duct means an unmetered-air lean code. Reconnect the battery cable. Start the Impreza and confirm a smooth idle, then drive it and rescan for codes. A post-job misfire on a boxer is usually a coil that isn't fully seated in its tube — push each one home again before suspecting the new plugs.
I've watched people get this wrong: A post-job misfire on a boxer is usually a coil that isn't fully seated in its tube — push each one home again before suspecting the new plugs.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
2017–2023
2017–2023
2017–2023
2017–2023
2017–2023
2017–2023
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