Car Battery Light ON and OFF while Driving -Causes (Explained)?

Fixing the red battery light flashing ON and off while driving can be a cause of frustration – it can be difficult to pinpoint the cause!

Some car owners for example have had their alternators and batteries replaced and yet the intermittent flashing of the car battery light was not fixed.

So in the post, I will share with you the most common causes and what you can do to fix the flashing battery light.

Hopefully, this post helps you save time and frustration in fixing this problem.

Car Battery Light On and Off – the different ways

It can show up in several ways while driving, it may last only a few seconds while in other cases, it lasts longer before going off.

In some cases, the on-time for the car battery light increases when you continue driving the car without fixing it.

You may be able to drive your car without any problem though your car’s engine may stop without warning.

Regardless of the frequency and timing, it is usually related to a problem with the car’s charging system.

The Normal Operation of Well functioning Car Battery Light

How does a well-functioning car battery light operate?

When you turn the ignition key to the start position, the battery light and a few other dashboard lights ( engine check, oil light) momentarily come on as the engine starts then go off.

When the ignition key is in the ACC position, all the dashboard lights including the battery light is off.

On turning the ignition key to the ON position, all lights on the dashboard light continuously.

The battery light should not light at all as you drive the car. Should it light whether steady, for a few minutes or intermittently on and off, this signals a problem with your car’s charging system.

What causes the Car Battery Light to come ON and OFF while Driving (7 common causes)?

A flashing car battery light indicates a problem with the car’s charging system.

There are several possible reasons why your car’s battery light may flash ON and OFF intermittently as you drive.

The 7 most common causes are:

  • a bad or failing alternator
  • a bad or failing car battery
  • loose or damaged cable connections at the battery
  • loose or damaged cable connections at the alternator
  • Poor earth or ground connections between the battery’s negative terminal and the car’s body
  • Connecting an appliance with a high power draw on the battery

In some cases, car owners have noted the On and OFF behavior after replacing an alternator or car battery.

While other times, the flashing battery light may start without any prior changes to the car’s electrical system.

So, it helps to think back to what changes you may have made to the car’s electrical system if any to help you resolve the problem faster.

Car battery Light On and Off – Is it Safe to Drive?

While you may be able to drive your car for several days with the battery light occasionally flashing on and off, you risk the car failing on you on the road.

It may suddenly stop and or fail to start when you least expect it leaving you stranded and needing a tow truck simply because the underlying problem – may be a bad alternator, battery, or loose cabling is not fixed.

So, look through the list of tips you can below if you are comfortable working with cars.

It can be something you can fix yourself or you can take it to an Autozone car professional car garage to fix it.

Either way, fix it as soon as is possible.

What to Do – Car Battery Light comes ON and OFF when Driving?

You will likely be able to drive on when the light comes on.

Here is a light of checks you can do that may help you fix the issue (in order of simplicity).

  1. Check for loose connections/ wiring on the battery and alternator terminals.

This is a good place to start – Inspect the connections of the cables to the battery and the alternator.

If you move them, are they firm or loose? You may need to tighten them

Are the battery terminals clean or do they have signs of corrosion – the powdery blue substance? Clean the corrosion off the terminals and tighten them.

Check the wiring harness that plugs into the alternator. Gently move the wires? Is the harness firmly plugged into the alternator? Are the wires in the harness firm? add photo.

2. Check the battery voltage

A fully charged 12V battery should measure about 12.7 – 12.8VDC.

If your battery voltage is lower, your car may have a charging problem or you may have a failing battery.

Consider having your car’s battery tested at an Autozone or a certified mechanic

3. Check the Alternator output

A functional alternator connected to the battery with the engine running will generate about 13.8 – 14.5VDC.

A considerably higher alternator voltage or low voltage may be a sign of a malfunctioning alternator.

You may have to have your alternator tested at the Autozone or a certified mechanic

Check out our guide on Overcharging of car batteries | Is it good or bad for the battery?

4. Poor earthing or grounding

Poor grounding – like a loose ground connection in your car can also result in erroneous interpretation of the battery voltage measurements by your car’s computer system.

Have you recently replaced the battery?

Might your car have a loose negative battery cable?

You can use a good-quality multimeter to measure continuity between the car’s body and the negative battery terminal.

For good grounding, the resistance will be zero ohms.

5. Check if you have recently connected any high-power draw accessories to the car’s electrical system.

High power appliances such as a car amplifier can drain the battery power causing the car battery light to flash ON and OFF whenever they are switched on.

You may have to add a second battery to fix this. Consult a qualified car professional though.

Final thoughts

If your car’s battery light comes ON and OFF, check for loose connections on the battery and alternator terminals.

You may also need to test the alternator and battery outputs to make sure they work fine.

Confirm that the car’s grounding is proper as this may cause erroneous voltage readings.

Also, .check if any high power draw accessories like a car amplifier may have been connected to the battery lowering the battery voltage and triggering the ON and off flashing of the Car battery light.

Hope this helps! Let me know in the comments below.

Related Posts

Leave a Comment