Parts for your 2004 Toyota Highlander-Ignition coils

2004 Toyota Highlander Ignition Coils

Ignition coils are absolutely used on the 2004 Toyota Highlander. Toyota’s 2004 Highlander Repair Manual for the 2AZ‑FE (2.4‑litre) and 3MZ‑FE (3.3‑litre V6) engines specifies a coil-on-plug (COP) ignition system for each cylinder. Toyota’s Electronic Parts Catalogue lists an individual ignition coil assembly per cylinder for these engines, and DENSO’s technical documentation identifies COP units as the OE design on both engines. So for this model year, coils aren’t just relevant — they’re essential.

On a 2004 Highlander, each spark plug has its own ignition coil mounted directly on top, delivering a strong, precisely timed spark without traditional high-tension leads. That setup improves reliability and spark energy, helping the Highlander start cleanly, run smoothly and sip less fuel. The 2.4‑litre four-cylinder runs four coils, the 3.3‑litre V6 runs six.

When coils age or cop a hard life, they can cause misfires, rough idle, sluggish acceleration and higher fuel use. The check engine light will often pop up with codes like P030x (cylinder-specific misfire) or P035x (ignition coil circuit). Because COP units sit right on the plugs, heat and oil contamination are the usual villains.

As part of regular servicing, it’s smart to inspect the coils whenever the spark plugs are out. Use quality iridium plugs at the correct gap and torque, and refit coil hold-down bolts to around 7–9 N·m. A tiny smear of dielectric grease on the inside of each coil boot can help future removal and ward off moisture. If a coil is cracked, oil-soaked or the boot is perished, replace it.

• Go OEM-quality (DENSO or equivalent) for best compatibility with Toyota’s engine management.
• If only one cylinder is faulting and the coil swap test confirms it, replace that coil, if multiple coils are the same age with recurring issues, consider replacing them as a set.
• Keep the plug tube seals and rocker cover gaskets in good nick to prevent oil ingress that kills coils.

Most owners can expect long service life from original coils, especially with fresh plugs at scheduled intervals. For a Highlander that feels perky, idles sweet as, and returns decent economy, healthy coils and plugs under the bonnet are a big part of the story.

How many ignition coils does a 2004 Toyota Highlander have?

The 2.4‑litre four-cylinder uses four coils, one per cylinder. The 3.3‑litre V6 uses six. Toyota’s coil-on-plug design means there’s no shared coil pack or leads, each cylinder gets its own dedicated unit for a strong, consistent spark.

What are the common signs a coil is failing on this model?

Typical symptoms include a rough idle, hesitation or lack of power, poorer fuel economy and the check engine light. Scan tools often show misfire codes like P0301–P0306 or coil circuit codes P0351–P0356. Swapping the suspect coil to another cylinder is a quick way to confirm the fault.

Should coils be replaced individually or as a set?

If testing isolates one bad coil, replacing just that unit is fine. However, on higher‑kilometre vehicles where coils are all the same age and multiple misfires are cropping up, replacing the full set can save time and repeated labour, especially when paired with fresh iridium plugs.