06/02/2026
Spark Plug
A spark plug is an ignition device that converts high-voltage electrical energy from the ignition coil into a spark inside the combustion chamber.
This spark ignites the compressed air–fuel mixture, creating controlled combustion that drives the piston downward and produces engine power.
🔴Working Principle
📌The battery supplies low voltage to the ignition coil.
📌The ignition coil steps it up to around 20,000–40,000 volts.
📌High voltage travels through the spark plug wire or coil-on-plug system.
📌Voltage jumps across the center electrode and ground electrode gap.
📌This jump creates a spark arc (~8,000°C) that ignites the mixture.
📌 Combustion pressure pushes the piston down, rotating the crankshaft.
🔴Spark Plug Construction
Key parts:
Center electrode – carries high voltage.
Ground electrode – forms spark gap.
Ceramic insulator – prevents electrical leakage and withstands heat.
Metal shell – screws into cylinder head and transfers heat.
Resistor – reduces electrical noise affecting ECU sensors.
📌 Heat Range Concept (Very Important)
Spark plugs must operate between 450°C – 850°C:
Too cold plug → carbon fouling, misfire.
Too hot plug → pre-ignition, engine damage.
Correct heat range ensures:
Self-cleaning temperature
Stable combustion
Long engine life
📌Common Spark Plug Fault Symptoms
Engine misfire
Rough idle
Poor fuel economy
Hard starting
Loss of power/acceleration
Increased emissions
📌 OBD-II Trouble Codes Related to Spark Plugs
Useful for diagnostics:
P0300 – Random/multiple cylinder misfire
P0301–P0304 – Misfire in specific cylinder
P0350–P0362 – Ignition coil circuit faults
P0171/P0172 – Lean or rich mixture affecting spark quality
📌Service Life by Type
Copper plug → ~20,000–30,000 km
Platinum → ~60,000 km
Iridium → up to 100,000 km
📌Professional Tip
Always check spark plug gap, color, and deposits—
they reveal engine health, fuel mixture condition,
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