The check engine light is on after changing the car battery? Here’s why

Replacing your car’s battery can be an easy task especially if you know a thing or two about the process. However, seeing the check engine light go on after replacing your battery can be a harrowing experience characterized by uncertainties.

It might leave you wondering if you carried out the process wrongly or damaged something in your engine that may cost a lot of money to fix.

So, why does the check engine light go on after a battery change?

The check engine light may go on after battery change because the new battery is faulty, undercharged, or because the sensor is unable to detect the new battery.

Additionally, the light may flash due to a wrong electrical connection that’s preventing the charging system from charging the battery with sufficient voltage(of at least 13.5 volts).

When you see the light flashing, you don’t need to freak out because it doesn’t necessarily mean that you’ve damaged the engine or at least something in it.

What Causes The Check Engine Light To Come On When Replacing The Battery?

The check engine light is connected to the Electronic Control Unit (ECU) that is connected to the battery sensor alongside other types of sensors within the car’s engine, as well as the battery management system.

The ECU serves as the computer of the car that ensures that the engine works optimally with optimal conditions. It accomplishes that by controlling several functions and processes including the battery management system(BMS).

Meanwhile, the battery sensor feeds the ECU with accurate data about the battery e.g the battery’s current, voltage, temperature, state of charge, and state of health, whereas the BMS precisely adjusts the necessary parameters to optimize battery functionalities and life.

If the sensor detects abnormal conditions with the battery system, it relays the wrong data to the ECU, which in turn triggers the check engine light to warn you that something is wrong with your battery.

This may be due to a faulty or undercharged replacement battery, or a poor electrical connection after replacing the battery. Don’t forget that a bad connection may hinder your charging system from charging the battery or at least hamper its charging capabilities, preventing it from supplying a charge of at least 13.5 volts to the battery during the charging process.

Or it could be that the sensor is just unable to detect the new battery. In that case, resetting your ECU may help correct the sensor so that it functions normally again.

Can a New Battery Cause the Check Engine Light to Come On?

The short answer is YES. This can happen if you put poor quality or undercharged battery with a percentage charge level considered too low into the engine.

Please note that if the new battery has a charge level lower than 75%, the sensor will interpret that as an abnormality and hence relay the information to the ECU, which will trigger the check engine light.

It doesn’t come as a surprise that some vendors sell poor-quality batteries as well as undercharged batteries with percentage charge levels lower than this.

If your check engine light is due to a poor quality battery, the only solution is to get a better battery. If it’s due to an undercharged battery, try charging the battery to up to 75% and above charge levels before putting it into the engine.

Do You Need to Reset the Car After Changing the Battery?

The short answer is: yes, sometimes. This is especially if the check engine light is being triggered by the ECU because the sensor just won’t detect the new battery.

In most cases, resetting the car’s computer will restore the sensor’s capability to detect the new battery. This will see the check engine light problem go away.

Does the Check Engine Light Reset On Its Own?

It can happen that sometimes the sensor may reset on its own to detect the new battery and that will cause the check engine light to shut off.


Having a flashing check engine light after replacing your car’s battery can be somewhat troubling. After all, you may be unsure if the problem is emanating from a serious mechanical issue that the car has developed after replacing the battery or something else.

But the good news is that you don’t need to freak out if you find yourself in that situation. Having the check engine light flashing after replacing your battery doesn’t necessarily mean that your engine has developed a serious problem.

Most of the time, it simply means that the new battery you put in the engine is faulty or undercharged. Other causes of this issue include a bad electrical connection or the battery sensor’s inability to detect the replaced battery.

Sometimes resetting the car may help especially if the light is flashing due to the sensor’s inability to detect the new battery. Other times, the sensor may self-reset and stop the check engine light from flashing.

Alternatively, you may need to get a better battery or charge the battery as necessary before putting it inside the engine.

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