1
Let the turbo engine cool and size up the job
Park on level ground, shut the engine off, and let it cool completely — at least an hour after driving. Pop the hood.
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2018–2024 GMC Terrain
2018-2024 GMC Terrain — Spark Plug Replacement
By Tom Becker ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
🔧🔧🔧 Advanced
45–60 minutes
$115 DIY
Save $335 by doing it yourself! Shop cost: $450
Quick answer: Spark Plug Replacement on a 2018–2024 GMC Terrain is rated Advanced and takes about 45–60 minutes. You'll need 5 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.
Quick Video Tutorial
Parts You Need
Total Cost
$115.00
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Correct spark plug set for 2018-2024 GMC Terrain; 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
Step-by-Step Instructions
Follow these steps carefully
2
Pop off the Terrain’s engine cover to expose the coils
Grab the front of the plastic engine cover and lift straight up — it’s held on by friction-fit rubber grommets over studs, no bolts. Set it aside. Underneath you’ll see the four ignition coils in a row along the top of the valve cover. The 1.5L and 2.0L both look nearly identical at this point, which is why checking your window sticker or the under-hood label matters when you buy plugs.
3
Disconnect the battery
Loosen the negative battery cable clamp with a 10mm wrench, lift the cable off the post, and tuck it aside so it cannot spring back onto the terminal. You will lose radio presets and the clock, and the transmission may shift differently during a short relearn drive afterward.
🔧 Mechanic's note — Tom Becker
I tuck the loose cable behind the battery hold-down — if it springs back onto the post while your hands are down in the plug wells, you'll know about it.
4
Unplug and unbolt the four 1.5T/2.0T coil packs
Press the release tab on each coil’s electrical connector and slide it straight off — work the connector, not the wiring. Then remove the bolt holding each coil down with a 10mm socket.
5
Pull the coils
Twist each coil gently to break the boot loose, then lift it straight out of the plug well. If a boot is stuck to the plug, work it free with a twisting motion rather than yanking — torn boots cause misfires.
🔧 Mechanic's note — Tom Becker
Quick word from me — I've been under there: If a boot is stuck to the plug, work it free with a twisting motion rather than yanking — torn boots cause misfires.
6
Extract the old plugs
Feed a 5/8-inch spark plug socket on a 6-inch extension down the well, seat it on the plug, and turn counterclockwise to loosen. Pull each old plug out with the socket’s rubber grip or a magnet.
7
Gap-check each new plug against the manual, not a guess
This is where you do not guess. Check the gap on every new plug with a feeler gauge against the specification in your owner’s manual or the emissions sticker on the underside of the hood — the 1.5T and 2.0T can differ, and aftermarket plugs arrive at whatever gap the factory set. Adjust gently by bending the ground strap only, never the center electrode. Many modern plugs come with a pre-coated thread finish, so follow the plug manufacturer’s guidance on anti-seize rather than adding any by default.
🔧 Mechanic's note — Ray Delgado
I've seen this exact mistake come through the shop: Many modern plugs come with a pre-coated thread finish, so follow the plug manufacturer’s guidance on anti-seize rather than adding any by default.
8
Seat the plugs by hand
Drop each plug into the well and turn it in BY HAND until the washer seats — if it binds early, back it out and restart it; cross-threading an aluminum head is a very expensive afternoon.
🔧 Mechanic's note — Tom Becker
I've found that small thing, big difference: Drop each plug into the well and turn it in BY HAND until the washer seats — if it binds early, back it out and restart it; cross-threading an aluminum head is a very expensive afternoon.
All Done!
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
- • Dropping a bolt or debris into an open plug well — blow the wells out before the old plugs come out.
- • Forcing a plug that resists on the way in — back it out and restart it by hand to avoid cross-threading the aluminum head.
- • Skipping the gap check because plugs are 'pre-gapped' — verify against the manual or under-hood sticker instead.
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2018-2024 GMC Terrain — Check Engine Light / OBD2 Diagnosis
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2018-2024 GMC Terrain — Replace Cabin Air Filter
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2018-2024 GMC Terrain — Replace Ignition Coil
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