2019 Toyota Highlander Spark Plug Spec Guide

As an ASE-certified master technician, I’ve serviced countless Toyota SUVs, and the 2019 Toyota Highlander is a frequent visitor to the bay for standard maintenance. Whether your Highlander is equipped with the 2.7L 4-cylinder, the robust 3.5L V6, or the Hybrid powertrain, using the correct spark plugs and proper torque is critical for fuel efficiency, emission compliance, and long-term reliability.

Here is everything you need to know about replacing the spark plugs in your 2019 Toyota Highlander.

Quick reference

*Note: Toyota recommends a 60,000-mile interval for the 2GR-FKS under certain severe duty or emissions scenarios, though standard iridium life is typically 120,000 miles. Always check your specific owner's manual.

Why the right plug matters

Modern Toyota engines are highly sensitive to spark plug heat ranges and electrode materials. Toyota exclusively uses Iridium-tipped spark plugs from the factory (supplied by Denso). Iridium is up to six times harder and eight times stronger than platinum, allowing for an incredibly fine wire center electrode. This lowers the voltage required to jump the spark gap, improving firing efficiency and reducing strain on the ignition coils.

Downgrading to platinum or copper plugs in a 2019 Highlander will result in poor fuel economy, potential misfires, and a drastically reduced service life. Always stick to the OEM Denso Iridium or premium NGK equivalents.

How to gap a spark plug

While most modern iridium spark plugs come pre-gapped from the factory, it is always a best practice to verify the gap before installation in case the plug was dropped during shipping.

When checking the gap on an iridium plug, do not use a traditional coin-style gapper. The fine wire iridium tip is extremely fragile and can snap off easily. Instead, use a wire-type gauge or a feeler gauge. If adjustment is necessary, use the bending tool on the gauge to apply leverage only to the ground strap. Never pry against the center electrode. Bend the strap slightly, then re-measure with the wire gauge until you achieve the correct specification (0.043" for the 2.7L, or 0.031" for the 3.5L).

Replacement procedure tips

The 2019 Toyota Highlander utilizes a Coil-on-Plug (COP) ignition system. Each spark plug has its own dedicated ignition coil bolted directly above it.

For the 2.7L 4-cylinder: Replacement is incredibly straightforward. The coils are right on top of the engine under the cosmetic cover.

For the 3.5L V6 (Standard and Hybrid): Because the engine is mounted transversely, the rear bank of three cylinders (Bank 1) is tucked tightly against the firewall. To access these rear spark plugs, you must remove the upper intake manifold (plenum). When doing this, always replace the intake plenum gaskets to prevent vacuum leaks upon reassembly.

• The Anti-Seize Debate: NGK and Denso both manufacture their plugs with a special trivalent metal plating that prevents thread seizure. Do not use anti-seize compound on the threads of these plugs. Adding anti-seize acts as a lubricant and can easily cause you to over-torque the plug, potentially damaging the aluminum cylinder head threads.
• Dielectric Grease: Apply a small dab of dielectric grease to the inside of the ignition coil boot before reinstalling. This prevents moisture intrusion and stops the rubber boot from sticking to the ceramic portion of the spark plug over the next 100,000 miles.

Known issues

Unlike the notorious Ford 3-valve engines that suffer from broken plug shells, Toyota's engines do not have systemic issues with spark plug breakage during removal.

However, the biggest "known issue" for the 2019 Highlander is the proliferation of counterfeit Denso spark plugs sold on massive online marketplaces. Counterfeit plugs use inferior metals that will melt under normal combustion temperatures, causing catastrophic engine damage. Always purchase your spark plugs from a reputable, authorized auto parts dealer or dealership.

Need plugs replaced? Find a shop on Repairius.