Are you unable to turn on your car's battery light while driving? Here's how to fix it

An unexpected light appearing on your dashboard is always a cause for concern. Your worries are more than doubled when you also don’t understand what that light indicates. 

So, in this article, not only will we talk you through what a battery light is, but also what the top 8 most common reasons why it may show up whilst you’re driving. 

It does NOT necessarily indicate if your battery has gone bad. It is a simple indicator to tell you whether or not your vehicle’s alternator is charging your battery. 

The auxiliary belt or serpentine belt drives your alternator, generating an electrical charge to drive your engine while you drive. Every time your car is started, your battery loses some of its charge. 

Therefore, if your vehicle detects that its battery is no longer being charged, it will illuminate your battery light as you’re driving. 

Broken auxiliary belts or serpentine belts are the most common reasons why a car's battery lights up while you drive. A worn or defective alternator, or its wirings can be the cause. A bad battery or dash cluster can be the cause in rare instances.

Your car's battery can go on for many reasons. These are only a few of many possible causes for your car's battery light to go on. Below is a list of eight most frequent reasons why your car's warning lights are on.

Índice de Contenido
  1. Why is my battery light on while driving?
    1. 1. Broken Auxiliary Drive Belt (Serpentine Belt). 
    2. 2. Failure of the Alternator 
    3. 3. Broken Alternator to Dash Cluster Wire 
    4. 4. Faulty dash cluster 
    5. 5. Faulty Battery 
    6. 6. Battery Terminals with Corroded Batteries 
    7. 7. Broken/ Corroded Motor Earth Strap 
    8. 8. Worn Alternator Pulley
  2. Conclusion 

Why is my battery light on while driving?

1. Broken Auxiliary Drive Belt (Serpentine Belt). 

Serpentine Belt Components

The most frequent reason that your battery light will illuminate while driving is because of this. If your auxiliary drive belt has broken, then it’s no longer able to spin your alternator, meaning there is no electrical charge being generated in which to charge your battery. This is a common fault that your vehicle will detect and notify you about. 

You may also experience other signs such as lost power steering or loss of air conditioner if your belt is worn. 

The process for diagnosing this fault couldn’t be simpler, carry out a visual inspection on the engine and it should be immediately obvious if your belt has snapped. As long as your vehicle hasn’t been driven for a prolonged amount of time without a belt, you should be able to get away with just replacing it and driving as normal.

Top Tip You should remove all debris and old belts from your engine bay. This could lead to problems later on if they get caught in cooling fans or pulleys. 

More information on how to diagnose it can be found here: Serpentine Belt symptoms

2. Failure of the Alternator 

Alternator Location

So, if your serpentine belt seems to be fine, the next component we look to is your vehicle’s alternator. There are many components inside your alternator that can fail. Your alternator will stop charging at the rate your vehicle needs, whether it has faulty diodes or broken windings. 

This is quite a technical diagnosing process, however, if you’re not comfortable working with electrics on a running engine then take your vehicle to a local garage. Many times, they will provide a special tester which will allow you to quickly diagnose the alternator. 

More information on how to check and diagnose your alternator can be found here: Alternator symptoms

3. Broken Alternator to Dash Cluster Wire 

Alternator Cluster Wire

It is more complicated to identify, but it has happened many times. This wire is usually a short 15-amp cable that runs to your dash cluster. It's susceptible to wear and corrosion. This will be connected via a standard connector to the alternator and then will go to your dash-cluster or to an ECU. 

This is the easiest method to identify the fault. Have your battery and alternator tested to make sure that they’re both operating as they should be. If there are no problems, you can check the wire. Carry out a visual inspection on the block connector fitted on the alternator’s back and make sure a good connection is visible. Then, inspect the wire for any corrosion or broken connections. Repair and start your car if any breaks or corrosion are discovered.

4. Faulty dash cluster 

Instrument Cluster

Although it is not the most common fault on the list, this one still occurs frequently enough that it deserves to be included. 

Usually, with a faulty dash cluster, you will also notice other faults such as faulty odometer readings or other illumination lights when they shouldn’t be and vice versa. 

You will need to bench test the dash cluster by a specialist to find out if it's faulty. 

5. Faulty Battery 

Car Battery Charger

Another common problem that would be indicated by your battery light illuminating whilst you’re driving is that your battery may be faulty. Your battery may not receive the electric feed from your alternator due to a shorted cell. You may notice a slow start of your car, particularly on cold mornings. 

To diagnose the problem, it is necessary to test your battery. An ordinary multimeter won't always show a damaged cell in a battery. However, most garages have a battery tester and can perform the test for a nominal fee. 

6. Battery Terminals with Corroded Batteries 

Corrosion Battery Terminal

A variety of unusual faults may be caused by corroded or loose battery terminals. Whilst it’s unlikely to, it can sometimes be the case that it will illuminate your battery light whilst your driving. 

Conduct a visual inspection on battery terminals in order to detect corrosion and ensure tight connections. Top Tip To prevent corrosion buildup, spray a little clear grease on your battery terminals. 

7. Broken/ Corroded Motor Earth Strap 

Car Ground Strap

Like the loose/corroded battery connections and a variety of other strange faults, a damaged or corroded ground strap could also lead to a wide range of problems on your vehicle. It’s a very uncommon but not unheard of fault that’s actually quite easy to check for.  It is common to find one between your engine and the body, and another between your car's battery terminal and the body.

Simply carry out a visual inspection of your vehicle’s earthing straps and check for any breaks or tears. At either end of the straps, it’s important that you check for a build-up of corrosion also as this could cause a poor earth connection. Top Tip To ensure a strong connection, remove fixing bolts. Next, reattach the strap to the car and tighten the bolts. 

8. Worn Alternator Pulley

Alternator Pulley Clutch

It is an uncommon fault on cars, but common in German vehicles. These alternators have a special pulley, which is only designed to spin in one direction. This design can prevent damage from the alternator, but it can also cause problems if it does go wrong. 

You can diagnose the problem by removing your auxiliary belt and manually turning your alternator pulley. You should see it spin in the desired direction. The pulley may need to be replaced if it does not spin freely in the direction of rotation. This can usually be accomplished without having to replace the entire alternator.


So, if your battery light illuminates whilst you’re driving, just be aware that your vehicle won’t run for very long – depending on battery health and what accessories you have switched on. 

Pull over as soon as it’s safe to do so and have your vehicle towed home or to a garage because by continuing to drive you run the risk of causing further damage to your engine. 

It’s important to have your battery regularly tested as it can lower the chance you get caught out with a fault such as this. 

This list is hoped to be of great assistance to you. Please feel free to return to it whenever you have to.

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