Back to basics: Testing, replacing starters and alternators

Starters and alternators are essential in powering the internal combustion engine. Issues with either component can spell serious consequences for a vehicle, ranging in severity – from slower starts to unexpected breakdowns and long-term electrical damage.

As vehicles and their service needs continue to evolve and shop offerings grow more complex, let’s bring it back to the basics with a reminder of how to identify and resolve electrical and charging system failures stemming from rotating machines.

A refresher on how starters and alternators work

To kick things off, let’s re-establish how starters and alternators are expected to perform.

The entire combustion process begins with the (appropriately named) starter. When you turn the ignition key or push a button to start a vehicle, the starter-solenoid coil delivers a strong electrical current from the battery to the starter. The starter motor will spin rapidly to rotate the engine’s flywheel, cranking the engine – a process that sucks air into the cylinders. Pistons begin moving up and down, spark plugs ignite the air/fuel mixture that’s building in the cylinders, and there you have it – a running engine.

The role of the alternator begins where the starter’s work ends. The running engine connects to the alternator’s pulley with a belt to turn the rotor shaft within the alternator. The rotor rapidly spins a series of electromagnets around a coil to generate Alternating Current (AC). This current is fed back into an element called a rectifier, which converts it from AC to Direct Current (DC). DC is what your car uses to power electrical components, like headlights and windshield wipers, as well as to recharge the battery as it runs.

Signs of trouble

There are a few telltale signs that something is wrong with your vehicle’s rotating machines. A clicking sound when you try to start the car or an engine that cranks slower or doesn’t crank at all can point to a weak starter. If your battery is frequently dying but appears to be in good health, your alternator could be failing to charge – in which case, you should notice a red battery symbol light up on your dashboard.

If your car fails to start or run at all, it could mean something’s wrong with your starter or alternator – but check in on your battery health first, as problems with both parts can stem from there.

Diagnosing and solving the problem

At the first sign of trouble with starting your vehicle, run a diagnostic scan. Modern scan tools, such as those from the Bosch ADS series, can generate diagnostic trouble codes (DTCs) in as quick a timespan as 30 seconds to a minute, narrowing a technician’s search for the root of the problem.

Before resorting to replacement, technicians should first test for potential power supply issues. Tools like the Bosch BAT 135 Battery Tester can be used to perform voltage ripple tests, where the technician gauges whether AC voltage is still being output by the alternator after the DC conversion process is completed. AC voltage at this stage of the process has a rippled appearance, hence the shorthand “alternator ripple.”

If alternator ripple is detected, this could indicate issues with the alternator’s rectifier or stator. If the rectifier or stator is determined to be the issue, you will most likely replace the alternator with a new or rebuilt unit available from your parts store.

Navigating part replacement

Before faced with a starter or alternator that needs replacing, it’s important for shop owners to source quality replacement parts. You don’t need to stock your inventory with a brand new alternator, as modern remanufactured parts offer quality you can rely on at often significantly lower costs. If you can, prioritize remanufactured parts that have been thoroughly disassembled, tested and reissued with OE core – the casing and main components that were original to the unit or car itself – instead of with separate components pulled from off the shelf. This is so you can rest assured the format function is identical to what it needs to be, as these molds originated with the vehicle.

Replacing the starter

Begin by disconnecting the negative battery cable to avoid any electrical risks, then jack up your car and support it with a sturdy stand. To maximize safety, consider a stand that prevents you from having to crawl beneath the vehicle to stabilize – such as the S03G Geared Jack Stand from OTC.

Move any wires or other components covering the starter out of your way, then use a small socket wrench to disconnect the battery cable from the starter. Grab a ratchet to unscrew the bolts from the starter, then once it’s free, remove it from the engine.

Put the replacement remanufactured starter where you removed the old one, securing the bolts you just unscrewed and replacing any wiring you had to undo. Finally, reconnect the battery and lower your vehicle from the jack. All set!

Replacing the alternator

As always, begin by disconnecting the negative battery cable and any additional wiring from the old alternator. Loosen the belt tensioner so you can remove the serpentine belt, and check for wear and tear on these components while you’re at it. It is highly recommended that if you see or suspect wear on the drive belt, you replace it – along with the tensioner assembly.

Grab a wrench to loosen the few bolts holding the alternator in place, then remove it from the engine. Retrace your steps with a replacement remanufactured alternator. Before reconnecting the battery, make sure it’s got decent charge – don’t overwhelm the replacement alternator by immediately tasking it with charging a low voltage battery!

The bottom line

A lot of these details will likely come as second nature to long-time repair professionals, but as our tools and technology continue to evolve, it never hurts to revisit the basics. Keep the conversation going in your shops and ask your team for their tips and tricks on servicing rotating equipment with ease – you never know what you might learn!