How To Check If Alternator Is Bad

How To Check If Alternator Is Bad

Modern automotive electronics is a marvel. Almost every amenities you find in modern cars are now powered by some sort of engineered electronics. In fact, manufacturers have found ways to incorporate all sorts of convenience features into realistic dimensions while keeping it all self-sustaining.

The most astonishing fact is that despite implementing electronics that far exceed what cars were originally intended for, we’re still using a fundamentally identical technology to generate electricity. An alternator supplies all the electrical energy needed for a vehicle while being driven off the combustion engine.

Other than fully electrified cars, most vehicles still run an alternator of some sort. The majority still uses a basic 12V (or 24V for commercial vehicles) alternator that’s driven from a drive belt by the main pulley. Even mild hybrids still run an alternator, albeit an unorthodox kind intended to provide assistance to the engine when required.

The fact of the matter is that while the electrical demands of modern vehicles are ever-increasing, alternator (generator) technology hasn’t improved a great deal. Open up an alternator from now and 2 decades ago, and you’ll see that the foundation has remained the same.

However, all of that increased load puts much more stress on a modern alternator. This means that alternators now play a much bigger role than ever before, and they can begin to experience failure sooner than ever. Contemporary cars integrate deft electrical energy management but when an alternator begins to fail the effects are profound.

Before knowing how to spot a failing alternator, it’s helpful to know how an alternator functions. A car alternator is quite a miracle. It’s expected to operate in a highly turbulent and straining environment continuously powering all of the vehicles electrics while offering trouble-free operation for ~100,000 miles.

In a car, the alternator’s function is simple. A car has a battery that supplies the required voltage and current to respective consumers, but a battery capacity is finite. While that wasn’t as big a deal a century prior, a modern car will not function with a dead battery. Most importantly, the electrical system must drive the starter, the ignition system, and the fuel system.

Therefore, the alternator’s purpose is to keep recharging the battery so that a car can maintain continuous operation. Because an alternator actually generates alternating current (AC), while a battery carries and supplies direct current (DC), the alternator must also transform its generated AC into DC.

Furthermore, to charge a car battery that operates at approximately 12.6 volts fully charged, the alternator has to supply more voltage than the battery. And this voltage must not be too little or too high, either will result in a malfunctioning electrical system. Thus, managing the system’s operating voltage is also part of an alternator’s function.

Finally, it’s the alternator’s job to be self-sustaining. This means that while it’s driven by the engine drive belt, it must power itself. This is why a failing alternator may stop charging the battery altogether because past the starting stage the alternator actually energises itself to charge the battery. When it stops supplying sufficient charge, the alternator should be able to inform the driver as well. This comes in the form of the battery light in your instrument cluster.

Symptoms of a bad alternator

The issue with most alternator failures is that prior to its failure, there might not manifest obvious symptoms. For the average car owner, a failing alternator will only be palpable once the battery warning light comes on. In fact, cars nowadays do such a good job at energy management that it can keep a car with a flawed alternator running until you reach the workshop.

Still, there are obvious ways to tell that something might’ve gone awry with your electrical system. It doesn’t necessarily pinpoint the issue, but it’ll help your workshop to diagnose the issue.

1) Hard Starting

This is quite a serious issue that might hint towards an alternator at the end of its life. Since an alternator’s job is to sustain extended vehicle operation by charging the battery, a failing alternator won’t sufficiently charge your battery.

The issue might develop from a reduced cranking speed to a no-crank condition. With a bad alternator, you might not be able to start your car once you park it for a short grocery run. However, a no-start or hard start does not single out the problem down to a bad alternator. That said, the chances are greater if your car is difficult to crank over once you park it for a short trip.

It’s a good idea to get this issue diagnosed immediately. Anything that causes a poorly performing starting system can be detrimental to your electrical system as a whole. Whether if it’s a starter on its way out or a battery that’s dying, it puts unnecessary stress on your engine electricals. Be sure to get the system checked as a whole once you get it repaired.

2) Odd vehicle behaviour

Because most of the vehicle’s electrical energy is supplied by the alternator once it’s running, a bad alternator will exhibit strange vehicle operation. Anything on your car that runs on electricity can perform poorly or unexpectedly once your alternator fails.

Some obvious signs will be a misfiring engine. A bad alternator might not maintain a sufficient charge level to run an engine properly. For example, the ignition coils might not provide enough energy to fire the spark plugs during high demands where a greater ignition charge is needed.

It’s also possible that the alternator can’t provide the current draw a fuel pump needs at higher operating ranges. In newer cars, a no-charge condition can introduce a whole host of trouble codes along with an insufficient battery charge. The vehicle’s computing modules won’t be able to perform optimally with unstable charging.

Alternator and Battery Tests

For some cars though, a failing alternator might be perceptible just by observing your headlamps carefully. Because the headlamps are a major consumer of charge current, a bad alternator can translate to dimmer lights. You might notice this as a flickering headlamp and varying brightness depending on your revs.

The other major current consumer in a vehicle is the climate control blower. Therefore, if your blower is suddenly unable to move as much air as it was before, that might indicate a failing alternator. In modern cars, this is part of an energy management strategy to maintain vehicle operation for as long as possible.

It’s also common for a car suffering from charging issues to be down on power for no apparent reason. The infotainment system will also switch off, as speakers are also a main source of current consumption.

3) Worrying noises from engine bay

This may be a bit difficult to notice for some, as a car’s engine is generally too noisy for most average owners to notice any peculiarity. Much less so a worn engine with various ticking and mechanical noises, or a modern direct-injection engine with a rowdy high-pressure pump.

It’s possible for an alternator issue to further develop into a loud noise that overwhelms the engine’s operating noise though. One that we might be familiar with is a rough, sandpaper-like metal-on-metal grinding noise. It sounds like the sound of gritting sand. This generally points toward a worn bearing that can complicate alternator failure.

The other noise that an alternator can produce is a loud, noticeably high-pitched whining. This noise occurs when the alternator is being overworked by the voltage regulator. When this occurs the alternator is being energised more than it’s rated for. You should get this issue diagnosed immediately.

Try not to confuse these noise with lifter tick.

4) Alarming smell from alternator

With an alternator that’s being overworked, it will also begin to overheat. In general, the alternator diodes can’t withstand too much heat before cooking and failing. If this happens, it’s often accompanied by the unmistakable smell of electrical fire or burnt wire.

5) Warning lights in the instrument cluster

Finally, this is overt but still needs to be said. The easiest way to tell that something might be up with your electrical system is a warning message being delivered in your instrument cluster. A charging issue is generally depicted by a red battery icon within the instrument cluster.

For some cars, this might be represented by an ‘ALT’ or ‘GEN’ symbol. When these lights illuminate, it generally points toward an issue with the alternator. It’s also possible for it to only light up briefly, or blink from time to time. If this happens, be sure to get it checked as an alternator failure might be imminent.

How To Check If Alternator Is Bad Red Battery Icon No charge

In older cars, the alternator’s voltage regulator is actually connected to the warning light. When the warning light lights up, this actually means that the alternator is not being self-energised and thus not charging the vehicle’s battery. This can happen whenever the alternator is not adequately charging the system and can’t provide charge to itself to sustain the vehicle’s operation.

With later cars though, the alternator is computer controlled, so it’s charging voltage is monitored by the on-board electrical system. This allows for more precise management of the charging voltage, so poor charging performance can be determined quickly and intelligently by the engine’s computer.

How To Check If Alternator Is Bad

Should your car exhibit any of the above symptoms, it’s always worth the effort to get your alternator checked out. The last thing you want is a failed alternator when you’re on a road trip. Modern cars incorporate comprehensive and automated self-test of the alternators through their diagnostic systems, but there are DIY methods to quickly determine the condition of your alternator.

1) Turn on your headlamps – Look for dimming

As mentioned prior, headlamps are a major current consumer. Therefore, any issue with the charging system itself can be identified just by observing the headlamps’ luminousity. You should either do this at a dark spot, as any changes can be seen easily.

With a faulty charging system, you’ll first notice that your headlamps will begin to flicker. With an alternator related issue, this flickering should vary depending on your engine’s RPM. If your headlamp becomes brighter as you give it some gas, that’s a good indication that something is wrong with your charging system.

Checking your alternator look for dimming headlights at night

2) Removing negative terminal – See if the car still runs

The other way to quickly determine an alternator’s charging capacity is by disconnecting the negative terminal of your battery while your engine is running. This means that the alternator would be managing the entire vehicle’s charge level. A strong alternator would be capable of maintaining engine operation.

However, with modern cars, it’s best that you avoid this test. The battery serves as a buffer to iron out the otherwise unstable charging current that remains even after rectification. This unstable current can hinder engine computer operation and even damage them. It’s also easy to burn out the alternator diodes and regulator if you do it for an extended period.

3) Voltmeter test – Watch for voltage drop

If you want a definite and relatively accurate method to determine the condition of your charging system, then your best bet would be a multimeter. Multimeters can be picked up at your local hardware store for cheap and tells you a lot more than observing your headlamps.

Before you start the car though, be sure to get a baseline of your battery condition. Measure the voltage of your battery without the ignition on. A charged battery should have above 12.0 volts available, ideally approximately 12.6 volts. Without a properly charged battery, then any charging tests you perform can be misleading.

After you’ve ascertained the voltage of your battery, you can do also do a quick cranking voltage test. If you have a min-max feature on your multimeter, start a recording and crank over your car. It’s fine even if the car starts. Take note of the minimum voltage registered while your engine is cranking over. This reading should be above 9.6 volts for a strong battery.

Finally, you’ll get a reading of your vehicle’s charging voltage. Allow some time for your vehicle’s charging system to stabilise and recoup from starting. Roughly 20 seconds is good enough. Then, take note of your measured charging voltage. Ideally, you’d want a reading between 13.5 to 14.5 volts.

It’s acceptable if your reading isn’t exactly within the charging voltage range. Different carmakers adopt different methods to regulate their alternator, check your manuals for the specific range of your car. Without any load on a charged battery, the reading should be around 13 to 14 volts.

You should always take a loaded test of your alternator. This is done by switching on all your major current consumers, including the blower, infotainment system, and headlamp. The charging voltage should increase to above 14 volts. Needless to say, readings above 15 volts or below 13 volts is a cause for concern, and you should get your charging system checked.

What should you do if your alternator is bad

You should never ignore signs that could potentially point towards an alternator failure. A bad alternator can quickly pile up into a bigger issue. However, there’s generally no need to panic, as any good battery should hold enough charge to last you the distance to reach a workshop.

If you drive a newer car, then there is not much you need to do manually. Most actions are taken automatically by the car’s computing unit to ensure that your car can be driven for as long as possible even without the alternator actively charging it.

If active energy management strategies are required, then a warning message should appear on the instrument cluster providing warnings. If you notice the heater going away or the blower speed reducing, then glance over at the instrument cluster. There should also be a noticeable lack of power. Consult a workshop if the battery warning light is on.

In older cars though, if anything out of the ordinary is happening you should pay attention to the instrument cluster. If the battery light is on, then minimise the electrical load by switching off any amenities you don’t need. This means the blower, radio, and heater if applicable. If necessary, maintain a fast idle (slightly depress the throttle at idle) to increase the charging capacity.

However, if your car cuts out while driving with the battery warning light on, then you should make an emergency stop somewhere safe. Don’t attempt to start your car and drive it again. Call for a tow truck and haul your car to a workshop you trust.

It’s important that you do not attempt to drive a car with a failed charging system. This is especially true for newer cars. For one, you risk damaging your battery by putting too much stress on it. It’s also plausible that running a bad alternator will damage sensitive electronics due to the unstable charging condition.

Crucially, in any new car, driving a car with a faulty charging system is potentially dangerous. Some contemporary engines are now running electric water pumps that can’t function optimally without adequate charge.

Furthermore, electrically-assisted steering systems and even brake-by-wire systems might not function properly without ample charging. These systems have fail-safes implemented to protect the driver in case of an abrupt failure, but it may still catch inexperienced drivers off guard.

Is it actually a bad alternator?

That said, the aforementioned symptoms can be misleading. It’s difficult to definitely determine the fault to be an alternator purely from the symptoms. These are typically signs that your electrical system isn’t functioning properly.  Further diagnosis is vital to accurately ascertain the failure point before you toss a new and expensive alternator at your car.

Hard Starting Diagnostics & How To Check If Alternator Is Bad

A car that cranks slowly does not immediately point towards an alternator. The likelihood is greater though if your car has a slow crank if you only park it for a short trip. Even then you still need a multimeter to condemn the alternator.

In most cases, car owners come back to their car after a few days or weeks of idle period then find that their cars don’t make a single noise when the key is turned. This is because the battery is completely drained. It’s normal for a connected battery to drain entirely when parked for months.

However, if your car won’t even crank after parking it for a few days, then the battery is the main suspect. That said, if you replace your battery, it’s pragmatic to request a parasitic drain test to ensure nothing is prematurely depleting your battery’s charge. An aftermarket radio or amplifier is often the culprit of excessive parasitic drain.

To check for a bad battery, you need a load tester. It’s an equipment that simulates a vehicle’s cranking load on a battery. A healthy battery should be able to maintain above 9.6 volts after 15-20 seconds of cranking time at 20 celsius. It’s time to replace your battery if it drops down to below 5 volts, as the starter would be barely capable of turning an engine over at such meagre voltages.

How To Check If Alternator Is Bad - Drain Test

It’s also possible that a slow crank is caused by a starter on its way out. Starters tend to be remarkably durable, so a sluggish cranking speed is often the first sign of a starter failure. At this point, it’s best that you refrain from further stressing the starter. Either opt for a tow or a push-start.

A common mistake people make when their car barely cranks over is they keep turning the key hoping for a miracle. This is an easy way to over-drain your battery and even risk burning out your starter, causing further irreparable damage to the starter.

Signs of a failing starter is the slow cranking speed no matter the battery charge or if it’s being jumped. In some cases, the starter relay may actuate and the starter draws current, but it doesn’t turn. That’s also a sign of starter failure. You may notice this from the cabin lights dimming when you turn the key.

An easy way to determine whether if your battery is at fault is by observing your cabin lights. If your cabin lights die out when you turn the key, your battery is on its way out. You can also pay attention to the sound of a rapidly clicking solenoid, which indicates that the battery isn’t supplying ample current to rotate the starter.

How To Check If Alternator Is Bad – Verdict

Due to the correlation between every part of an engine’s electrical system, it’s essential that you get a charging related issue checked out immediately. However, it’s important that you don’t just throw parts at your car, as it’s common for charging related issues to be misdiagnosed without thoroughly performing tests.

Acknowledging the symptoms can avert further damage. Therefore, if something feels off in your car, it’s best that you visit a local workshop immediately. It might just save you from a bigger bill in the future.

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