The starter motor: the highest-current circuit in the car
An engine cannot start itself. It has to be turned fast enough to draw in mixture, compress it and get the first combustion to happen — a couple of hundred rpm on a petrol engine,...
The electric motor that turns the engine over until it fires, engaging the flywheel ring gear through a pinion that retracts once the engine runs. It is distinct from the starter relay, which merely switches its supply, and from the starter/generator, which replaces it entirely on mild hybrids.
Its faults are usually blamed on it and usually are not. A starter draws hundreds of amps, so everything in that circuit loses voltage only when the current is flowing — a battery that reads a healthy resting voltage, a corroded terminal, or a tired earth strap all produce slow cranking with a sound motor. Voltage drop under load is the measurement that separates them; a continuity check proves nothing here. The engine can be the cause too: thick, wrong-grade or very cold oil makes it genuinely harder to turn.
Stop-start changes the arithmetic completely. A conventional starter might see thirty thousand operations in its life; a stop-start vehicle can reach that in a year, so those cars use reinforced starters and matched AGM or EFB batteries. Fitting an ordinary battery or a standard starter to one is a common shortcut that fails early — and the module notices, because it measures cranking speed and will disable stop-start rather than risk a slow restart at a junction.
Also known as: starter, cranking motor, start motor, starter mota, self starter
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An engine cannot start itself. It has to be turned fast enough to draw in mixture, compress it and get the first combustion to happen — a couple of hundred rpm on a petrol engine,...
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