Why Won’t My Car Start? Starting and Charging System Failure Symptoms

When your car won’t start, most people are quick to jump to conclusions about what might be happening, while others are quick to call a tow truck to get the vehicle to a shop. But basic diagnosis of a failing charging or starting system on your car can be relatively simple using nothing more than basic tools and process of elimination. If you’re asking yourself “Why won’t my car start?”, let O’Reilly Auto Parts go over some of the symptoms you might experience when a battery, alternator, or starter goes bad and how to test these components to help you begin your diagnostic journey.

What Does an Alternator Do?

The charging system on your vehicle is relatively similar in design across most cars, trucks, SUVs, and more. It consists of the alternator, which is driven by a belt to convert mechanical power from the engine into electricity to recharge the battery and run the vehicle's electrical systems. Though this may be oversimplified when compared to the charging systems on modern vehicles, these are the basic components that make up most charging systems.

What is a Car Starter?

Your vehicle’s starting system is also relatively consistent with the types of starting system components found across most of the vehicles on the road. It is made up of the starter, which has a gear and shaft that engages the flywheel or flexplate to turn over and start the engine, as well as a solenoid that may be built into the starter or installed separately in the engine compartment. As with the charging system, the battery cables and battery are also major components of the starting system. Knowing how your vehicle’s starting system is laid out can help you begin your diagnosis.

Car batteries are relatively simple parts, and they are discharged and recharged thousands of times over their life. With time, or due to environmental conditions, the battery in your car can suffer damage and begin to wear out. The extreme heat of summer can also cause damage to the battery which decreases its capacity, but in many cases, you may not be aware of the condition of your vehicle’s battery until you attempt to start your car in the cold of the winter. This is why O’Reilly offers free battery testing to help you determine the condition of your battery before it leaves you stranded.

The first symptom of a worn-out car battery is reduced capacity for cranking and charging. This can manifest as an engine that cranks over slowly, especially in cold weather. You may also find that your battery no longer can achieve a "fully charged" status, and cannot produce the appropriate amount of voltage, which should be about 12.6 volts. You can test the voltage at your battery terminals using an automotive multimeter to see if the battery is holding an appropriate resting voltage. If it is less than 12 volts, it’s a clear sign that your car battery may no longer have its full capacity, but this could also indicate a failure elsewhere in the charging system. Learn more about using an automotive multimeter with this helpful article.

The next symptom of car battery failure is a complete failure to start, or only hearing a “click” from the starter when you turn the key. This is typically a result of a reduction in the battery’s available cranking amperage, which, even if the battery is holding at 12.6 volts, could be reduced due to battery wear. The only accurate way to test this is to perform a load test, either using a battery load tester or using an automotive multimeter and reading the voltage drop as someone else turns the key. It is also important that you check your car’s battery terminals for signs of corrosion and clean them with a battery brush if needed because a buildup of corrosion can prevent power from reaching or exiting the battery and may cause charging difficulties and starting failure.

Car batteries may also leak and bulge due to physical damage over time. Corrosion on the battery terminals is caused by the battery acid reacting with the lead of the terminals, which can eventually cause erosion and poor contact. If your battery case is leaking or bulging, it is recommended that the battery be replaced as soon as possible to prevent further damage and ensure consistent starting power. Your local O'Reilly Auto Parts can test your battery for free, and can even recharge your battery if it is severely discharged to ensure an accurate test. If you’re ready for a new battery for your car, check out our line of Super Start® batteries to deliver the power, performance, and reliability you demand from your car.

Alternators are driven by the engine belt, and this will be one of the first places you’ll want to look, especially if you’ve noticed noise from near the alternator. In some cases, this could simply be caused by a worn-out belt or tensioner, and you may notice other symptoms like engine overheating due to a water pump that is not receiving the power it needs to operate. Checking the belt’s condition and tightness can help you diagnose whether the problem is with the alternator or the belt itself.

In some cases, removing the belt and attempting to spin the alternator pulley by hand can help you determine if there is increased resistance that may be causing the belt to slip and the alternator to fail to charge. Some alternators are also equipped with decoupler pulleys that act as a clutch to turn the alternator on and off, and this pulley can fail and prevent the alternator from turning. Voltage regulators are often built into the alternators of some vehicles that act as a metering device to prevent the battery from overcharging, but many alternators on modern vehicles are regulated externally by the engine control unit. If the voltage regulator fails, it may cause too little voltage to reach the battery to recharge it, or in some cases, it could allow the full voltage from the alternator to overcharge and damage the battery.

If the battery does not have enough charge when you try to start your car, you may jump to the conclusion that the battery is at fault. Though this may be true, it could also be a sign of an underperforming alternator. If you jump-start your vehicle and the alternator is not working as it should, it may run for several minutes until the charge in the battery has been depleted and then stall. This is because the ignition system relies on power from the alternator to operate while the engine is running. Without a constant supply of power from the alternator, the ignition system draws power from the battery until it is too depleted to continue running the engine.

The best way to test an alternator is by using an automotive multimeter set to DC voltage and measuring the battery voltage before and after the engine is running. As discussed previously, the battery should have about 12.6 volts, which is on the low side of the spectrum for smaller and lower-output alternators. Even if you need to jump-start the vehicle to take the reading, with the engine running you should have around 14 volts at the battery if the alternator is working as it should. If you have significantly more or less power at the battery terminals, it may be a sign that the alternator, voltage regulator, or battery cables are damaged. Inspect your battery terminals and the connection to the alternator. If you’re not comfortable performing this test yourself, O’Reilly Auto Parts also offers free alternator testing on or off the vehicle. If you can get your vehicle to a local store, or simply remove the alternator and bring it inside, we can test your alternator and help you determine if it needs to be replaced, and recommend the right Ultima® alternator for your vehicle.

As parts of the starter wear out, a variety of symptoms can present themselves, but most include your vehicle not starting. If the starter motor is worn, or if there is corrosion on the battery or starter cable terminals, you may simply not get enough power flowing through the starter to get it to crank the engine over. Often this will also include an audible “click” noise as the starter shaft extends, but the starter may not have enough power to turn the engine. Inspecting the cables and connections at the battery and the solenoid can help you determine whether the problem might be the starter or a separate component. If your vehicle has an external starter solenoid that is not connected to the starter body, it may also be possible to test the solenoid directly.

The gear of the starter can also suffer damage from the thousands of times your vehicle may have been started in its lifetime. This can cause grinding noises as the teeth of the starter gear struggle to align with the gear teeth on the flywheel or flexplate. If this gets bad enough, or if the starter gear is damaged suddenly, you may instead hear a click and a whirring noise as the starter gear spins but does not contact the flywheel. This could also be due to damage to the flywheel, so it’s important to inspect the condition of both your starter gear and flexplate while you have your vehicle disassembled.

In some cases – especially if your starter is severely worn – you may not hear any noise at all when you turn the key. This could indicate that the starter isn’t receiving power, but you can test the power connections with an automotive multimeter to be certain that is the case. This could also point to a problem with the starter relay, ignition switch, solenoid, or other parts of the starting system. O’Reilly Auto Parts offers free starter testing, either in or out of the vehicle. If you remove your starter and bring it in, we can bench test the starter to determine if it is working as it should. If the starter shaft and gear fail to extend, or if it is cranking slowly once it has extended, we can recommend the best Ultima® starter for your repair.