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HomeTips & GuidesCharging System Warning Light: Causes and How To Fix It

Charging System Warning Light: Causes and How To Fix It

A car’s charging system primarily consists of an alternator, battery, wiring, and voltage regulator. The ECU monitors these aspects in real-time and, should anything go wrong, will throw an error, making the charging system warning light turn on.

This light usually turns on when your car solely runs on battery power. And without the battery recharging, your vehicle can only run for a limited time before the power source runs out. 

Here’s all you need to know about this warning light, including how to reset it.


A charging system warning light

What Is a Charging System Warning Light?

The charging system in vehicles begins with the alternator, which the engine spins to generate electricity.

 A voltage regulator ensures the alternator output voltage remains constant despite load and input voltage fluctuations.

This alternator supplies power to vehicle components while maintaining the required charge level in the battery.

So, if everything is okay, you will get no warning light on the dashboard. 

Some car models display a green battery symbol to indicate all systems are healthy.

Charging system and check engine warning lights simultaneously on

Charging system and check engine warning lights simultaneously on

But if the warning light glows red, the charging system has a significant failure and no longer recharges the battery. So, it needs immediate fixing.

Some vehicles are clever enough to indicate if the issue is not as serious by making the warning light glow yellow. 

This color indicates the battery charge level is low. It can recover to green/off or turn red should the issue persist.

What Causes the Charging System Warning Light To Turn On?

A red charging system warning light means the battery is not recharging. The causes of this failure include the following.

Dead Battery

A car battery has an operating lifespan of 3-5 years, and its health gradually declines towards the end. 

So, if you’ve not replaced the battery for the last three years, first check its health.

Most maintenance-free car batteries have an eye or “state of charge” indicator that should be green if the battery is healthy.

 If clear or black, the battery might need a replacement or charging.

A technician replacing a dead car battery

A technician replacing a dead car battery

Another way to determine if you have a bad battery is by measuring its voltage using a voltmeter or multimeter

A healthy battery should have a voltage reading of 12.4-12.7V when the engine is off. And when cranking the engine, the voltage should not drop below 9.6V.

Faulty Alternator

If the battery is okay, the most probable culprit is a bad alternator.

 Driven by a serpentine belt, the alternator converts rotational motion from the crankshaft pulley to generate electricity.

Most alternators have a built-in voltage regulator, meaning a malfunctioning unit could be due to a faulty voltage regulator.

A car alternator with the serpentine belt connected

A car alternator with the serpentine belt connected

The only way to tell if the problem lies in this component is to measure its voltage output. 

Most regulators limit the output to 14-15V in passenger cars and 28-29V in HGVs and large trucks.

Repair or replace the broken alternator if the multimeter readings indicate a lower number.

Damaged Drive Belt

As stated earlier, the serpentine belt is responsible for spinning the alternator using the rotational force from the crankshaft

Like other vehicle components, this belt wears over time by developing cracks, then snapping if not replaced.

A broken serpentine belt

A broken serpentine belt

As it cracks, the belt also loses tension. Most cars have belt tensioners to keep it tight around the pulleys. 

So, slipping might not occur. But if the belt snaps, the alternator won’t generate power.

Loose Battery Cables

Loose battery cables on the terminals hinder the power coming in from the alternator to recharge the battery. 

They should be tight on the terminal, and the terminal should be firm on the lug.

Corroded Battery Terminals

Salts forming on the battery clamps or lugs can also hinder the power flow coming in from the alternator. 

Maintain the battery regularly by cleaning the terminals using baking soda and water to eliminate the green, white, or blue substances.

A corroded battery terminal

A corroded battery terminal

Wiring Issues

The wiring harness transferring the power from the alternator to the battery might have cuts or corroded wire sections that hamper the electric current supply.

Accessory Overloading

Over-accessorizing your vehicle without installing a larger alternator to match the increased power draw can turn on the charging system warning light.

This issue happens when you power these components, making them draw all the current produced by the alternator. 

So, there won’t be any left to recharge the battery, meaning its voltage will drop gradually.

Accessories like light bars, winches, and subwoofers can cause this issue when you turn all of them on.

Faulty Computer

Although uncommon, a faulty computer can cause this issue. So, if you check all the other issues above and everything looks good, check the electronic control unit for current error codes.

A vehicle’s ECU

A vehicle’s ECU

How To Fix/Reset a Charging System Light

Through troubleshooting and testing, you might determine that the computer throws the charging system warning light erroneously. 

You can fix or reset the issue using the following steps.

You must have an OBD II scanner to access the diagnostic trouble codes saved by the ECU.

Step 1: Connect the OBD II Scanner to Your Vehicle

Connect the OBD II 16-pin plug to the port under the steering wheel, then turn on the ignition to initialize the scanning.

A basic OBD II scanner

A basic OBD II scanner

Step 2: Key in the Relevant Data

Enter the required data, including the vehicle’s make and model. 

You might have to key in the VIN or engine type. After that, give the scanner some time to scan the diagnostic system. 

Step 3: Analyze the Error Codes

After scanning the system, the device should list the current and past error codes. Ignore the latter. 

Analyze the current error codes by Googling their meaning.

Step 4: Fix the Issues and Reset the Computer

Once you’ve determined the root cause of the error codes, fix the issue, reset the system, and scan for other DTCs. 

Everything should be clear if there are zero faults, including the charging system warning light.

But if all fails, you can replace the ECU or reprogram it. 

Also known as remapping, the latter option requires technical expertise, but it might be cheaper than replacing the ECU.

Replacing the ECU is not a plug-and-play installation.

 You must go to an authorized auto repair shop to program the computer to the specific car model.

Is It Safe To Drive When the Charging System Light Is On?

It is safe but can leave you stranded in the middle of nowhere. Remember, this light turning on means the battery is not recharging. 

Without enough power from the alternator, the vehicle can only run for a short time before the battery dies.

Engines need electrical power via the ignition coils to ignite the air-fuel mixture. So, without power, the motor won’t run. 

Depending on the vehicle, you can drive for 30 minutes to an hour before running out.

Wrap Up

Depending on the cause, charging system warning lights can be simple or challenging to fix.

Issues like loose battery cables and corroded terminals are easy to rectify. Battery replacement is also easy but will dent your pocket a little. 

However, alternator, computer, and wiring issues are challenging to solve.

So, get to the bottom of the problem by troubleshooting the error to know where you lie. 

Check out this alternator wiring article to help you fix the issue if it is on this part. 

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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