The primary function of the spark plug is to ignite the air-fuel mixture within the combustion chamber under any operating condition.Checked 2026-08-12
Spark plugs and ignition coils
The parts that make and deliver the spark; on modern engines each plug has its own coil.
Also called: spark plug · ignition coil · coil-on-plug · coil pack
What it means
Definition
NGK, an OE plug maker, states the plug's job: the primary function of the spark plug is to ignite the air-fuel mixture within the combustion chamber under any operating condition. The high voltage to do it comes from an ignition coil. Older engines ran that voltage through plug wires from a shared coil; DENSO describes the modern coil-on-plug arrangement as requiring no high-tension ignition cable, fitting neatly into the engine's spark plug bore.
Why a buyer cares
What it changes
A misfire code names a cylinder, and on a coil-on-plug engine that points at one plug and one coil rather than a shared component — which is why misfire is often a small repair rather than a large one.
In practice
Where you meet it
On maintenance schedules and invoices, and behind misfire codes on a scan printout.
Two things that look alike
Not the same as
On a coil-on-plug engine there are usually no plug wires at all — the coil sits on the plug.
Read next
Related terms
Where this comes from
Sources
requires no high-tension ignition cable, fitting neatly into the engine's spark plug boreChecked 2026-08-12
The DENSO quote is a clause, not a full sentence. Replacement intervals are deliberately absent — they are per-vehicle.