Glow plugs are electric heating elements utilized in diesel engines to initiate combustion within cold cylinders. Installed within the pre-combustion chamber or directly into the cylinder head, they raise the air temperature to facilitate ignition of injected fuel. Typically constructed of a high-resistance alloy encased in a durable metal sheath, glow plugs require precise electrical current and operate for a defined duration during engine start. Modern designs often incorporate ceramic heating elements for faster warm-up and extended lifespan. Failure manifests as hard starting, excessive smoke, and potential misfire.