Quick answer: Spark Plug Replacement on a 2016–2021 Hyundai Tucson is rated Moderate and takes about 1–2 hours. You'll need 7 tools for this job, and parts cost about $41. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name |
Part Number |
Price |
Buy |
| Spark plugs (correct heat range) |
— |
$35.00 |
|
| Dielectric grease |
— |
$6.00 |
|
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
1
Confirm your engine (2.0L Nu vs 2.4L Theta II) and lift the cover
Park the Tucson on level ground and let the engine cool fully. Confirm which engine your 2016–2021 Tucson has before buying plugs: the 2.0L Nu GDI (base trims) and the 2.4L Theta II GDI (higher trims) are both four-cylinders with coil-on-plug ignition, but they use different spark plug designs — check the emissions sticker under the hood for the engine code. Disconnect the negative battery terminal with a 10mm wrench. The plastic engine cover lifts straight up off its rubber grommets on both engines, exposing the four coil packs in a row along the valve cover.
2
Unplug and unbolt the four coil packs in order
Remove the 10mm hold-down bolt from each coil and lift the coils straight up out of the plug tubes, setting them down in cylinder order so each returns to its own hole.
3
Blow out the plug tubes and remove the old plugs
Remove the rags and blast compressed air down each plug tube to clear the grit that collects there — this step is non-negotiable, since anything left behind drops straight into the cylinder when the old plug comes out. Fit a 5/8-inch (16mm) spark plug socket with a rubber insert onto a 6-inch extension, seat it fully on the plug hex, and break each old plug loose counterclockwise. Spin them out by hand and inspect: on these GDI engines, a light tan or gray deposit is normal, while heavy carbon buildup on the 2.4L can hint at the oil consumption these Theta II engines are known for.
🔧 Mechanic's note — Tom Becker
The compressed-air blast is the most skipped step in every plug job I see, and grit falling into an open cylinder is how a Saturday plug swap becomes an engine teardown. Thirty seconds per tube — don't skip it.
4
Verify every plug gap against the factory specification
Check the gap of each new plug against the specification printed on the emissions sticker under the hood or in the owner's manual — never invent or guess a gap value. Slide a wire-type or feeler gauge between the center and side electrodes and feel for a slight drag on the correct gauge. Adjust only the side electrode if a plug is off, and never pry against the center electrode on a fine-wire plug. Pre-gapped plugs can shift in shipping, so check all four even if the box claims they're ready to install.
5
Hand-thread the new plugs, then seat per the box instruction
Lower each new plug into its tube inside the spark plug socket — never drop it, since the electrode bends on impact — and thread it in by hand using only the extension. You should feel it spin smoothly with minimal effort; any binding in the first turns means cross-threading, so back it out completely and restart. Once finger-tight, finish seating each plug per the instruction printed on the plug box, typically a fraction of a turn past finger-tight for washer-seat plugs. The Nu and Theta II heads are aluminum and strip easily, so never apply heavy ratchet force.
🔧 Mechanic's note — Ray Delgado
I've learned: aluminum heads do not forgive a forced plug. If it binds in the first two turns, it's cross-threading — back it all the way out and restart. The five minutes that costs beats a helicoil repair every single time.
6
Grease the boots and reinstall the coils and connectors
Press each coil back down onto its plug until you feel it nest onto the terminal, reinstall the 10mm hold-down bolts snugly, and reconnect each electrical connector until the locking tab clicks — then tug gently to confirm.
🔧 Mechanic's note — Tom Becker
Click means clicked — I tug every connector after latching it. The number-one post-job misfire on these Tucsons is a connector that looked seated but wasn't, and you'll chase it for an hour before checking the obvious.
7
Refit the cover, reconnect the battery, and test drive
Press the engine cover back down onto its grommets until it sits evenly with no rocking, then reconnect the negative battery terminal. Start the engine — it should fire right up and settle into a smooth idle within seconds on either the 2.0L or the 2.4L. Take the Tucson for a short drive with a few stops and steady cruising; if it idles rough or the check-engine light comes on, a coil connector or the battery terminal is the likely culprit. Recheck the bay for stray tools before closing the hood.
All Done!
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
- • Buying 2.4L plugs for a 2.0L Tucson or vice versa — the Nu and Theta II GDI engines use different plug designs.
- • Reconnecting a coil connector without the tab clicking; the Tucson will idle rough and set a misfire code on the first start.
- • Cross-threading a plug by starting it with the ratchet — always hand-thread into the aluminum head first.
- • Leaving the engine cover loose on its grommets, where it rattles and can contact the hot exhaust manifold area.
