Starter & Alternator Testing at O’Reilly Auto Parts

An alternator is designed to provide continuous power to the various electrical systems in your car, including the radio, lighting, instrument panel, and more. It also ensures the battery is kept healthy and fully charged.

The alternator and battery work together to provide the power needed to keep all the systems in your vehicle working as they should. When the engine is running, the alternator is driven by the serpentine belt and crankshaft pulley to also provide the power needed to deliver spark and keep your engine running.

Newer alternators may also be designed with a larger capacity to support modern electrical amenities such as power windows, navigation units, infotainment systems, and heated seats. Since an alternator is such a crucial part of your charging system, it’s important to pay attention to signs of alternator failure to help keep your vehicle running as it should.

Yes, your alternator helps charge the battery by supplying direct current (DC) power, but the alternator is not intended to be a battery charger. Your alternator is only meant to restore charge to the battery that was used when you started your engine, or if you used electrical accessories while the engine wasn't running.

If the battery is extremely discharged or dead and you have to jump start your vehicle, it causes the alternator to have to work harder to get the battery back to a full charge, which can result in alternator failure. Restoring a complete charge to a battery that is at 50% charge using only your alternator can take up to 11 hours of driving to bring the battery up to 90% or more, and during that entire duration the alternator must run at peak output.

If your battery is completely dead or extremely discharged, it's usually better to plan to recharge your battery fully using a battery charger, as it is possible that the alternator could also fail. If you need to have your battery recharged and don’t have your own battery charger, visit your local O’Reilly Auto Parts. We not only test batteries for free, but can also safely recharge them in-store.

Why Do Alternators Fail?

While most alternators are designed to last anywhere from 40,000 to 100,000 miles, they can wear out and fail internally over their life. The lifespan of your vehicle’s alternator can be affected by a number of variables, many of which are not within your control. Environmental conditions and high temperatures, debris and breakdown of moving components, or a buildup of contaminants can cause parts of an alternator to wear out and eventually fail. Electronic components may also suffer damage due to moisture, or your alternator may be overworked attempting to charge a failing battery.

• Damaged Alternator Bearing

  With constant heat, stress, and friction, an alternator bearing can wear and may no longer spin as freely. A bad alternator bearing can make it harder for the engine to turn the alternator and limit the amount of power generated, which can prevent your battery from being recharged. In extreme circumstances, the alternator bearing may lock up and lead to belt noise and damage, eventually causing the belt to snap and resulting in other symptoms like overheating, loss of power steering, air conditioning, and more.

• Fluid Leak

  Oil leaks from the engine or the power steering hoses or pump can drip into the alternator, coating the internal components with oil and limiting conductivity. This can damage the mechanical and electrical charging components of the alternator, causing it to fail or no longer produce adequate power to recharge the battery or keep the engine running.

• Using Jumper Cables Incorrectly

  When jump-starting a car, it’s important to connect each cable on both batteries to the appropriate terminals to avoid reversing the polarity. Crossing or hooking up the cables backwards can damage your alternator and battery, as reversing the polarity for even a moment can cause voltage spikes, sparks, and damage. Need guidance on properly jump-starting a car? Check out our helpful How-To resources on how to jump-start a car battery.

• Personal Driving Habits

  If you are a driver that loves to use their vehicle’s electronic accessories while idling, this can unfortunately put a strain on the alternator and impact its lifespan with time. Though this is rare, alternators typically work best above 1650 RPMs, so limiting the time spent using high-load accessories like lights, blower fans, radios, and more at idle can reduce the risk of alternator failure.

If your car isn't starting or running correctly, your alternator may be failing. The alternator keeps your battery charged and powers your car's electrical system, and it should produce between 13.5 to 14.8 volts when the engine is running. Replacing a faulty alternator quickly can prevent further damage to your car's electrical system and save you from having to replace a dead battery.

Symptoms of a Failing Alternator

• Visible Signs of Alternator Failure

  • Car won't start: The engine won't turn over, or the battery is dead.
  • Warning lights: The battery light or Check Engine light is on.
  • Lighting issues: Headlights are dim, excessively bright, or flicker

• Sounds and Smells

  • Whining, squalling, or screeching: These sounds may occur during startup, and may point to alternator or belt damage.
  • Clicking, rattling, or scraping: This could be a sign of a loose bearing.
  • Burning smell: A smell like burning rubber could indicate overworked wiring or a slipping serpentine belt.

• The Role of the Voltage Regulator

  A common cause of alternator failure is a bad voltage regulator. This component controls the power sent from the alternator to the rest of the electrical system, ensuring that it doesn't exceed a safe voltage.

  • Integrated vs. External: On some cars, the voltage regulator is built into the alternator, requiring the whole unit to be replaced if it fails. In modern vehicles, it's often a separate component regulated by the car's engine control unit (ECU).
  • Effects of Failure: A failing voltage regulator can send too much or too little voltage. Too little can cause the car to stall or die while running, while too much can overcharge the battery or damage other electronics.
  • Battery Overcharging: An overcharging battery might smoke or emit a sulfur-like smell due to the water inside evaporating.

• How to Check It

  You can use a multimeter to measure the voltage at your battery terminals. If the reading is above 14.7 volts or below 13.7 volts with the engine running, it may indicate a problem with the alternator or voltage regulator. If you’re not comfortable testing your alternator yourself, ask for free alternator testing at your local O’Reilly Auto Parts.

A starter is an electric motor that works to convert electrical energy into mechanical energy to start your vehicle. Powered by the battery, a starter motor is engaged when the ignition switch is turned to the Start position, and turns over the engine by engaging the geared flywheel or flexplate and spinning the crankshaft.

The starter solenoid, which is often mounted to the starter itself, receives the signal from the ignition switch to connect battery voltage to the starter, extend and spin the starter gear, and then retract the shaft and gear when the engine has started. Unlike an alternator that is constantly working while the engine is running, starters disengage once the engine has started and the key is returned to the run position to prevent damage to the flywheel or starter gear.

Why Do Starters Fail?

Problems with your vehicle’s starter can be caused by normal wear and tear, or may point to a larger issue with the starting system, and it’s important to understand why starters go bad. Often, starters simply fail due to demanding conditions, heat, and prolonged use, although there can be a few other variables that lead to starter failure.

• Bad Starter Solenoid or Relay

  • Solenoid: The solenoid acts as a switch that temporarily sends power from the battery to the starter motor. It's often found on the outside of the starter and is exposed to high temperatures, which can cause it to fail. Since the solenoid often can't be serviced separately, you'll usually have to replace the entire starter as a unit.
  • Relay: The starter relay works like a solenoid but can be replaced separately. It's typically located in the engine compartment's fuse box.

• Worn Internal Windings

  The starter motor has internal windings that produce the torque needed to spin the engine. Over time, these windings can wear out due to heat and prolonged use.

  • Symptoms: The starter gear might not extend or spin. You may hear a clunking or clicking sound if the gear extends but lacks the power to turn the engine.
  • Diagnosis: If you experience these symptoms, the starter likely needs to be replaced. You can have the starter bench-tested at any O’Reilly Auto Parts location to confirm the issue.

• Pinion Gear Teeth Wear

  The pinion gear's teeth mesh with the flywheel or flexplate to crank the engine.

  • Causes: The teeth can wear down or break off, especially if the starter is engaged while the engine is already running.
  • Symptoms: A damaged gear may fail to make adequate contact with the flexplate, causing a whirring sound without cranking the engine or a grinding sound on startup.
  • Diagnosis: You may need to remove the starter to inspect the teeth of both the pinion gear and the flywheel or flexplate for signs of damage.

• Incorrect Starter Installation

  Improper installation can cause various problems.

  • Loose bolts: The bolts that hold the starter in place also help create a proper electrical ground. If they are loose, it can cause poor electrical contact and misalign the starter, potentially damaging the flywheel and starter gear.
  • Over-tightened bolts: Tightening bolts too much can crack the starter housing or a non-conductive terminal, causing electricity to arc and not reach the starter motor.
  • Missing hardware: Some starters require specific shims or spacers to maintain proper alignment. Failing to use this hardware can lead to damage.
  • Fix: Always check the service manual for the correct torque specifications when installing a starter.

Starter failure is common due to demanding conditions, and a bad starter will typically exhibit a few symptoms before it dies completely. The most common sign that your starter is dying is that the engine won’t turn over when you turn the key or press the ‘Start’ button. This could also be caused by a dead battery, or may point to an issue with the starter, ignition system, or other electrical components. Over-cranking a starter also generates a great deal of heat and can potentially shorten the life of the starter motor.

Get Free Starter & Alternator Testing at O’Reilly

At O'Reilly Auto Parts, we offer a range of free services to help you diagnose and repair your vehicle's starting and charging systems. If you suspect a problem with your starter or alternator, bring your car, or the starter or alternator itself, to any O'Reilly Auto Parts location. Our experienced parts professionals can test these components while they are still on your vehicle. If your car won't start, you can bring in the starter or alternator for a free bench test on our specialized equipment to get a fast, accurate diagnosis.

Visit your nearest O'Reilly Auto Parts store to speak with one of our knowledgeable professionals and get the parts and services you need to get your vehicle starting reliably again.