You’ve probably heard it at the garage that something is wrong with the ignition coil, but what is an ignition coil anyway? We explain it here! An ignition coil causes the spark plugs to spark. This creates combustion in the cylinder, which causes the engine to run. The ignition coil thus converts a low voltage from the spark plug wires to a higher voltage. (an ignition coil is also called a transformer). This will spark the spark plug and allow the engine to start. An engine will not start without a coil. The engine will not start even if the ignition coil is defective.