Your Vehicle's Starter System

Think magic is only for magicians? Think again. You make magic happen every day with a simple turn of your vehicle’s ignition key or a press of the start button. Presto: the engine comes to life, seemingly like magic! No magic words required.

While you may know how to make your vehicle start, do you know exactly how it happens? It may seem simple, but it is a pretty complicated process dependent upon a number of components, all of which have to reliably and accurately work together to start your vehicle’s motor.

An automotive starter is used to rotate an internal combustion engine at approximately 150-200 rpms to begin the combustion process. To prepare an internal combustion engine to start, it must be cranked over so that fuel and air are sucked into cylinders. This mixture of fuel and air is then compressed in the combustion chambers preparing it to be ignited by a spark provided by the ignition system.

Most starters are mounted at the bottom of the engine area either on the left or right side where the transmission and engine connect. On modern vehicles, the starter typically includes the starter motor and starter solenoid as one assembly. However, on older vehicles, the starter solenoid is typically mounted separately on the inner fender well or near the battery in the engine compartment.

While it is correct to say the basic principles of the starter are the same today as they were when the first starter was designed, many specifics of starter design have improved considerably. For example, the pole pieces, which become powerful magnets when electricity flows through the field coils that are wrapped around them, have been replaced in most modern starters with permanent magnets. Since the energy required to magnetize the pole pieces is not needed, the starter uses less power from the battery and is more efficient.

Also, the direct drive design has been replaced in most modern starters with gear reduction drive designs. The off-set gear reduction design allows for smaller, lighter, and more efficient starters to produce the same amount of torque as the earlier direct drive starters while using less energy from the battery. The pinion gear is no longer connected to the armature shaft.

The powerful electric starter motor does the cranking. The small pinion gear engages with the teeth on a flywheel or flex plate that is bolted to the rear of the crankshaft. Flex plates are used with automatic transmissions, and flywheels are used with manual transmission vehicles.

The starter electrical system that controls the starter operation is comprised of an ignition switch, neutral safety switch (automatic transmissions only), clutch safety switch (manual transmissions only), battery, battery cables, anti-theft system, computer, key fob, the starter motor, and the starter solenoid.

The starter motor needs a heavy electric current, which it draws through heavy gauge cables from the battery. The main starter motor power is supplied directly from the positive side of the battery via the positive battery cable. The starter is designed to utilize this 12-volt, high amperage power source to provide the power to turn the engine.

Once the safety criteria are met by the neutral or clutch safety switch, electrical current is fed to the solenoid by turning the ignition key to the crank position or pressing the ignition start button. A trigger wire generates an electrical signal which is initiated by the ignition switch. This circuit supplies electricity to the starter solenoid which then activates the motor portion of the starter.

There are several common problems that can occur in the starter system, most of which result in unusual noises or no noise at all. Common noises associated with starter system problems include a whirring or spinning sound, buzzing sound, clicking sound, clunking or banging noise, grinding or grating noise, labored slow cranking, or the absence of any noise at all.

When the starter doesn't work or makes unusual noises, the state of charge of the battery should be tested, battery terminals inspected, battery cables checked, and all starter system electrical connections inspected for tightness and corrosion. One of the symptoms of a weak battery is the dash lights or headlights becoming dim when the starter is engaged.

The next step should be to test the starter control circuit. Battery voltage should be measured at the starter solenoid control terminal with the key in the crank position or the start button engaged. If there is no voltage, the problem is most likely in the starter control circuit (ignition switch, starter relay, neutral safety switch, clutch safety switch, control wire, security system, or key fob).

If there is proper battery voltage at the starter solenoid control terminal when the key is in the crank position or the start button is engaged, and the starter still won’t operate, the starter motor or solenoid may be faulty. Engine mechanical problems may also prevent the starter from cranking and can be determined by manually turning the engine’s crankshaft.

The starter system should be inspected at least annually. If you are considering purchasing a vehicle the starter system should be inspected prior to purchase. An ASE certified technician can quickly and thoroughly listen to and evaluate the vehicle’s starter system components to verify normal operation and provide you with peace of mind.