Alternator Or Battery Failure – Failure Symptoms With Testing

Alternator Or Battery Failure - Failure Symptoms With Testing
Alternator Or Battery Failure - Failure Symptoms With Testing

Having a alternator or battery failure is bad new, because they are both components of the charging system.

That makes diagnosing a alternator or battery failure, a bit tricky. Because, the electrical power in your vehicle, comes from both places.

And, because they both work together, if you have a alternator or battery failure, one will affect the other.

So, having a alternator or battery failure, can be an expensive repair. But, if you could narrow down the problem yourself, you can save money.

Quick Basics

Using the process of elimination, find the culprit by bypassing the battery’s role and jump-starting your car.

So, if the engine starts, but dies immediately, your alternator probably isn’t keeping your battery charged. Next, if a jump or boost, starts your car and keeps your car running. But, the car can’t start again off of its own power, a dead battery is probably your answer.

Alternator Function And Failure

You may think that the battery powers everything in your vehicle, but that’s not the case.

The battery provides electricity needed, for the starter motor to start the engine. When the engine is running, the alternator generates energy, to feed the electrical system and recharge the battery.

That’s why, an alternator failure, can easily lead to a bad battery.

After the battery starts the vehicle, the alternator takes over in charging it, while the vehicle is running. So, when the alternator goes bad, the battery, begins to compensate for the power the alternator should have generated.

This is because, the battery is not designed to supply power, for extended periods of time. Many people, even professionals, are quick to assume the battery is bad. But, this can be a costly assumption.

Alternator Or Battery Failure - Function - Failure Symptoms With Testing
Alternator Or Battery Failure – Function – Failure Symptoms With Testing

So, the alternator keeps things electrically charged and going. If it fails, you’re stuck. And, it can go bad slowly or suddenly. So, if you know the warning signs, you can get the alternator replaced, while it’s slowly going bad.

Here are some of the things you should know.

If the alternator dies, the battery doesn’t get recharged. So, any power used, is not replaced. However, when the engine is running, the alternator should charge the battery. And, also provide sufficient electrical power to the vehicle.

Consequently, the battery serves as a backup.

Sometimes, the vehicle requires more electrical power. than the alternator can provide. As a result, the battery covers the difference. Excessive demand, because of so many accessories, on at the same time can cause this. It all takes electrical power, putting a strain on the alternator, making its job even harder.

Battery Function And Failure

The easiest way to know if you have a bad battery, is when the battery light illuminates on the dashboard. The signs of a dead battery are usually obvious. Because, when you insert the key in the ignition and turn it. You will hear nothing at all when the battery is dead.

Alternator Or Battery Failure - Function - Failure Symptoms With Testing
Alternator Or Battery Failure – Function – Failure Symptoms With Testing

If the battery is going bad, you may just hear, a clicking sound when you turn the key. First, conduct a visual inspection of the battery. And, look for corroded leads or split wires.

Alternator Or Battery Failure Symptoms

Lights Going Dim Or Flickering

So, the failing alternator symptom most drivers recognize, is dim or flickering lights. This is really obvious when headlights are on at night. But, also noticeable in dash lights and the center dome light. If the lights brighten as (RPM)s pick up, that’s even more of a sure sign.

Service Engine Soon Light

Another obvious sign is the one, your vehicle tries to tell you. When the alternator starts to go, it can light up a “Check Engine,” or a battery icon indicator.

Odd Noises And Vibrations

The serpentine belt could have stretched with age. And, as a result, may not be spinning the alternator pulley effectively. This typically results in a squealing noise. On the other hand, the internal bearings can wear out, causing a growl or grinding noise.

Weird smells

An alternator works in conjunction with a system of belts. If a belt is not turning freely, the excess friction will cause the belt to heat up. Then, produces a burning rubber smell. If you catch a whiff of a smell, similar to that of an electrical fire. Consequently, this could indicate that the belt, is slipping on the alternator pulley.

Electrical Power Issues

Electrical vehicle equipment, like power seats or windows, may be slow to operate. Without enough power, sometimes the device will not function or will suddenly stop working. All because of, a alternator or battery failure.

Engine Stalling

If the engine suddenly cuts out while driving, it could be an alternator issue. Consequently, fuel injectors needs a good amount of electrical power and without it, the engine quickly stalls.

Dead  Or Drained Battery

Without a functioning alternator, the vehicle quickly uses up all of the battery’s capacity, leaving it drained. Pop the hood and check the battery and you might think you’ve found the culprit. But, even with a new battery, a malfunctioning alternator, will quickly leave you stranded again.

Alternator Or Battery Failure – Diagnosing And Testing

If you have a “Check Engine” light, connect a code reader to the diagnostic port. If you find code P0562 system low voltage, you are very likely have a failing alternator. Get it checked out, before it fails entirely.

Battery Warning Light On Dash
Battery Warning Light On Dash

If you suspect a failing alternator, but don’t have a warning light, check the condition of the belt. If it is glazed and slightly burned looking, that is an indication that it is slipping. As a result, the metal-on-rubber friction heats up the belt, quickly wearing it out.

Worn Alternator Belt
Worn Alternator Belt

If everything looks good under the hood, grab your multimeter. Make sure the vehicle is parked on level ground, with the parking brake on. Don’t forget to wear your safety glasses, when checking for a alternator or battery failure.

Set the meter to 20V DC. Connect the positive lead, to the battery positive terminal. And, negative lead, to negative terminal. It should read, around 12.6 volts.

Start the engine and carefully check voltage again. This time it should be at least 14.2 volts, if the alternator is healthy and charging the battery. If voltage is good, turn on the headlights, interior lights, radio, heater, and any other electrical load.

Charging Voltage Chart
Charging Voltage Chart

The meter should still display, above 13 volts. If any of the voltages are below spec, it’s a strong case for a new alternator. Finally, check all your cables for corrosion or a loose connection.

What Not To Do

If you’re tempted to test an alternator, by disconnecting the negative battery cable, don’t do it. A good alternator may indeed keep the engine running. But, it was never a good test. In the pre-computer days, you could pull it off without damaging anything. Today, you risk frying every electrical device in your vehicle.

The second you disconnect the battery, the voltage regulator pegs the alternator to put out maximum power. But, with no battery in the circuit to act as a buffer, the alternator can put out up to 150 volts, depending on engine rpm.


So, your battery supplies power, that travels through the starting system and turns the starter motor. Once the engine is running, the alternator sends power back to recharge the battery. Also, it supplies power for your vehicles electronics. Finally, diagnosing a alternator or battery failure, is not rocket science. So, take what you have learned here, and start saving money.

Thank You !