2015 Toyota Highlander Spark Plug Specifications

As an ASE-certified master technician, I’ve seen how a simple component like a spark plug can be the difference between a smooth-running engine and a frustrating, inefficient one. For the 2015 Toyota Highlander, using the correct spark plug and following proper installation procedures are key to maintaining its legendary reliability. This guide covers everything you need to know.

Quick Reference

Why the right plug matters

Your Highlander’s engine was designed from the factory to use high-quality, long-life iridium spark plugs. This choice isn't arbitrary; it's about maximizing efficiency, longevity, and performance.

• Electrode Metal: The 2015 Highlander uses plugs with iridium-tipped fine-wire center electrodes. Compared to older copper or platinum plugs, iridium has a much higher melting point and is incredibly hard. This allows for a very fine electrode, which reduces the voltage required to create a spark. The result is a more consistent and powerful spark, leading to better fuel combustion, smoother idling, and a longer lifespan—often exceeding 100,000 miles.
• Heat Range: Every spark plug has a "heat range," which determines how quickly it dissipates heat from the firing tip. A plug that is too "hot" (dissipates heat too slowly) can lead to pre-ignition (detonation), which can cause severe engine damage. A plug that is too "cold" (dissipates heat too quickly) can develop carbon fouling, leading to misfires. Sticking with the OEM-specified Denso plugs ensures you have the correct heat range for your engine.

How to gap a spark plug

Modern iridium plugs, like the Denso models specified for your Highlander, come pre-gapped from the factory. The fine-wire tips are delicate and can be easily damaged.

That said, it's always wise to verify the gap before installation, as plugs can be dropped or mishandled during shipping. Do not use a coin-style gapper tool. The sliding ramp can put pressure on the fine-wire tip and damage it. Instead, use a wire-style or feeler gauge. Gently slide the correct gauge (0.043 in) between the center electrode and the ground strap. If it fits with minimal drag, the gap is correct. If adjustment is needed, carefully bend only the ground strap (the curved piece of metal over the tip), never prying against the center electrode.

Replacement procedure tips

The 2.7L and 3.5L engines in the 2015 Highlander both use a modern, efficient coil-on-plug ignition system, which eliminates the need for a distributor and spark plug wires.

1. Coil-on-Plug Removal: To access the plugs, you must first remove the ignition coils. Disconnect the electrical connector by pressing the release tab. Then, remove the single 10mm bolt holding the coil in place. Gently twist the coil back and forth while pulling straight up to release it from the spark plug.
2. The Anti-Seize Debate: Most modern NGK and Denso plugs feature a special trivalent plating (it looks like a dull chrome finish) that provides anti-seize properties. The manufacturers state that adding extra anti-seize compound to the threads of these plated plugs is unnecessary and can lead to over-torquing. The lubricant effect of the compound can cause you to stretch the plug shell, potentially leading to a broken plug on a future replacement. For the OEM Denso plugs, install them clean and dry.
3. Dielectric Grease: While you shouldn't put anti-seize on the threads, applying a small dab of dielectric grease to the inside of the coil boot (where it contacts the spark plug's porcelain top) is a best practice. This grease is a non-conductor that prevents voltage leaks, seals out moisture, and keeps the boot from getting stuck to the plug, making future removal easier.

Known Issues

While some vehicles are infamous for spark plug problems—such as the Ford 3-valve Triton engines, known for 2-piece plugs that break off in the cylinder head, or certain GM engines with sensitive ionization-sensing ignition coils—the Toyota 1AR-FE and 2GR-FE engines are not among them. The conventional, one-piece, high-quality iridium plugs used in the 2015 Highlander are robust and reliable. Issues like cracked porcelain or broken plug shells are exceptionally rare on these engines when the plugs are installed correctly and not over-torqued.

Need plugs replaced? Find a shop on Repairius.