2018–2024 GMC Terrain
By Tom Becker ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
Save $260 by doing it yourself! Shop cost: $320
Quick answer: Replace Ignition Coil on a 2018–2024 GMC Terrain is rated Moderate and takes about 1 hour. You'll need 5 tools for this job, and parts cost about $60. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| ACDelco Ignition Coil | 12635672 | $50.00 | |
| ACDelco Spark Plug | — | $10.00 |
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
Read the codes first — P0301 through P0304 tells you exactly which cylinder is misfiring, so you only replace the failed coil. Gather a ratchet with sockets for the cover and coil hold-down bolts, plus the correct coil-on-plug for your engine. Let the engine cool.
Lift the plastic engine cover straight up off its mounting grommets. Set it aside where it can't fall onto the fender. Underneath are four identical coil-on-plug units in a row on the valve cover, one over each spark plug.
Find the coil on the misfiring cylinder. Press the release tab and slide the connector straight off — never yank the wires. Replacing more than one? Work one cylinder at a time or label each connector so the wiring can't get mixed up.
Each coil is held by one small hold-down bolt at its base. Remove it with the correct socket and set it where it can't roll away. Every bolt threads into aluminum — track them all and avoid cross-threading on reassembly.
Pull the coil straight up — twist gently if the boot is stuck, no prying against the valve cover. Inspect the boot for cracks or burn marks. Check the empty well: oil pooled around the plug means the valve cover gasket is leaking.
I've learned to oil pooled in that plug well is the valve cover gasket talking, not the coil. Slap a new coil on an oil-fouled plug and you'll be doing this job again within the month — fix the leak first.
Confirm the new coil matches the old in shape, height, and connector. Press it straight down into the well until it seats fully onto the plug. Reinstall the hold-down bolt snug — overtightening strips the aluminum threads. Push the connector on until it clicks.
Press the engine cover back onto its grommets until flush, then reconnect the negative battery terminal. Start the engine and let it idle — it should idle smoothly with no check-engine light. If a code is still stored, clear it and take a short drive.
I've learned: A misfire code that survives a fresh coil isn't a bad coil — it's the plug, the injector, or the wiring. Don't throw another coil at it; diagnose instead.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
2018–2024
2018–2024
2018–2024
2018–2024
2018–2024
2018–2024
