Reset Car Computer After Replacing Battery – How To Do It?

by Conner Mckay

Are you having a problem resetting a car computer after replacing battery? If this is the case you are at the right place. After replacing the car battery, the car computer can be annoyed and can throw an error or two and display a check engine light on the dash. In this article, we are going to explain to you how to handle these problems quickly and effectively.

The car computer has to be reset when you make changes to the components in your vehicle that are connected to the computer. But why should the computer be reset? The computer has to be restarted and returned to the factory settings to be able to learn the new settings and the check engine light to be removed from your dash.

Some computers are self-learning and they remove all the error messages from your dash, while other car computers need to be reset for them to continue working properly. In this article, we are going to help you out in doing precisely that. Because this is a problem that is troubling a ton of car owners who don’t know what to do in this situation. But we are going to clarify everything for you.

In this article, we are going to explain everything you need to know when it comes to the problem of resetting your car computer after replacing the battery. First, we will start from the basics and then we will move forward and explain how to reset the car computer after replacing the battery. Then we will discuss the costs of doing this. So, without further ado, let’s dive into the article.

Car Battery

The car battery is the battery that helps you start your car and power the accessories in your vehicle. The battery is a simple design that has been with us for more than 100 years and is still the number one choice when it comes to internal combustion engines.

The car battery is storing electricity that is produced by the alternator. The alternator is powered by the serpentine belt. Then this energy is used to do the initial start of the engine and also power accessory units like a radio or the dome lights. Without batteries, it will almost be impossible to crank the car.

There are still ways to crank an engine without a battery, but that would be going back in time and trying some manual methods. And you don’t want that. That’s why the batteries were invented to ease the use of cars and make driving more enjoyable.

The average six-cell battery that cars are using is usually rated at somewhere between 12 to 13.5V of power. This battery power is enough to start most cars and pickup trucks. The bigger the truck or car the bigger the battery is needed to start the car.

Yeah, but how to reset the car’s computer after replacing the battery? We are going to discuss that topic later in this article. After we cover the ECU, these things have to be clarified before we move on to some more complex topics.

How Long Does A Car Battery Last

As with other components in our cars, the battery has a lifespan. On average a battery lasts for 2 to 5 years. The more you drive your car and the more the battery charges the longer it will last.

What is killing a battery is if the car is driven less frequently. This allows for the internals of the battery to lose their characteristics. This affects the battery’s health and it tends to degrade and lose its juice much quicker than if the car is driven regularly.

That’s why you should drive your car more often and make sure that your battery is in good health. Diving like this will make it last for 4+ years with no problems.

Also, if your battery is relatively old, you should replace it as a preventive measure. Because it can fail all of a sudden and you might end up stranded on the side of the road. That’s why you should bear this in mind.

Also, it is useful to have a multimeter and measure the battery capacity every now and then. This multimeter tool is going to tell you a lot when it comes to your battery and how much life has in it. A good battery usually has more than 12V of power. But if the voltage is lower then this can mean that there are some issues with the battery on your car.

In this case, you will have to replace the battery and then look to reset the car’s computer after replacing the battery. That is something that we are going to cover a bit later in this article. But first, let’s learn what is an ECU?


The ECU is the car’s computer. Modern cars have computers inside that regulate everything. Without this computer, driving a modern car would be impossible and the car will not run.

The ECU gives directions to different components on what to do and also gathers a lot of information from sensors and other measuring tools to adjust the running of the car based on the conditions.

The positive side of the ECU is that it observes and adapts, it’s like a human brain inside of your car. The ECU is so smart that reads all the data from the sensors goes through all of this data and then adjusts the operation of the engine based on this information.

Reset Car Computer After Replacing Battery

When the ECU sees a change of components and their values do not match it will show a check engine light. Similarly with the battery. If the ECU is seeing a new battery in your car that has more power in it compared to your old battery that barely made 10V. It will show a check engine light. In this case, you will need to learn how to reset the car computer after replacing the battery. And how you can do this work? We will learn later after we cover the symptoms of a bad ECU.

Also, similarly with the sensors, when these sensors go bad or you replace a sensor you will receive a check engine light. You will not know why this light turns on in the first place. That’s why you need to troubleshoot and later in the article when we will cover how to reset the car’s computer after replacing the battery, we will show you how to use an OBD2 scanner to get rid of these annoying errors.

Bad ECU Symptoms

When the ECU goes bad it develops some symptoms that you are going to notice while you drive your car. The computer doesn’t go bad quite often but when it does, the work of the engine and all of the symptoms in the vehicle can go bad and this will result in poor engine performance from the vehicle. But what are the symptoms of a bad ECU? Let’s find out.

We elaborate on the symptoms because developing a check engine light on the dash is not quite a normal reaction from the computer. Since the car computer will not develop some problems when you replace a car battery. If it shows some errors then it could mean that there is something wrong with the computer as well.

Reset Car Computer After Replacing Battery, Symptoms #1: Check Engine Light

If the car shows up with a check engine light for no reason or it shows a check engine light after you install a new battery then this could mean that there is something wrong with the computer. It’s either the computer is bad or it is confused.

A normal battery swap should not result in a check engine light on the dashboard and problems. The computer should learn by itself that there is a new battery and reset itself. But sometimes it doesn’t do that and you might have to experience some unpleasant situations like this with the check engine light.

Later in this article, we are going to explain how to reset a car computer after replacing a battery in detail. After we cover all of the symptoms of a broken ECU.

Reset Car Computer After Replacing Battery, Symptoms #2: Engine Misfiring

Frequent misfires in the engine as well can also indicate a bad or failing ECU unit. This is caused because the computer is not working properly and bugged out.

A failing ECU can be extremely difficult to diagnose since you only get the readings from the sensors that are located in the car. There is no ECU unit health check.

That’s why these symptoms like a check engine light and misfires can confuse with other problems. Like bad spark plugs or bad engine coils. Since these components are very often attributed to misfiring issues. That’s why you need to make sure that they are in perfect working order to prove that the computer is wrong.

But how can I check if the computer is wrong? The only way to check if the computer is bad is to remove the components one by one and test them with a multimeter. Testing them with a multimeter tool will tell you what really is going on inside of your engine. And if the computer is wrong and it needs replacing or resetting.

Resetting the car computer after replacing the battery is the easiest thing that you can do in this case. Because often the computer can get confused and cause problems with your vehicle. Later in this article, we are going to explain how you can address that.

Reset Car Computer After Replacing Battery, Symptoms #3: Engine Does Not Start

If the engine doesn’t like to start, then it is very likely that you have a computer problem or a starter issue. The only way to see which of them has gone bad is to test the starter with a multimeter tool and see if the starter is any good. If the starter is good then you also need to test the solenoid.

This starter solenoid is a crucial component that when it fails can develop issues and prevent the starter from turning on. The solenoid is transferring the power from the battery to the engine.

Also, if the car computer is broken the engine could still crank. But it is unable to start since a lot of crucial componentry that turn on will not turn on in this case and the engine will be dead.

The only way to revive it will be by changing the car computer. Which in this case can be very expensive, or trying to reset the car computer. Later in this article, we are going to teach you how to reset your car computer after replacing the battery. But first, let’s cover all of the symptoms of a bad or an ECU that needs resetting.

Reset Car Computer After Replacing Battery, Symptoms #4: Performance Loss

Another problem with a failing ECU is that this problem can cause severe power loss. Especially if the ECU cuts out some important components that are needed to keep the car moving.

These systems can be connected with fuel supply or ignition. The car will highly likely switch to a limp mode to protect the components. But if the ECU is not in proper order, you know that it needs resetting and the only way around this will be to learn how to reset the car’s computer after replacing the battery. Something that we are going to elaborate on in-depth in the next chapter.

Resetting the computer is one of the key things that you need to know when you have a problematic computer unit in your vehicle. If the car computer doesn’t like to adapt and learn the new settings you have to do it by yourself. If it still doesn’t remove the check engine light you will probably need a new car computer. And that is something that we are going to cover later of how much is a car computer for your vehicle.

How To Reset Car Computer

Now we come to the most important part in which we will learn how to reset the car’s computer after replacing the battery.

If you have replaced your battery and you still get a check engine light then this chapter is perfect for you. We will share some invaluable information on how you can overcome this issue and enjoy your car. So, what’s the catch? There are two ways to reset a car battery. One of them is done manually and the other will involve messing with the diagnostic tool. Which of them works the best? Let’s find out.

Reset Car Computer After Replacing Battery

1. Remove The Positive Terminal

The simplest trick in the book to reset a car computer is by removing the positive terminal from the battery. To remove the terminal, you will need a small wrench to access the bolt that is holding the battery clamp.

Get a wrench that will fit the size and just loosen up the terminal. Then remove the cable in order not to touch the terminal.

Once removed, leave the car to sit like this for 5 minutes. Leaving the car without power will make sure that everything drains and the computer turns off. It is also useful to try to turn on the radio or other components that drain power to make sure that no electricity is left inside of the system.

After the time passes, reconnect the battery cable to the terminal. Tighten up the clamp and make sure that everything works properly. After this step, all of the systems should be turned on and there should be no more check engine light on the dash.

If this method doesn’t solve the problem for you to reset the car computer after replacing the battery. Make sure that you go through the next method.

2. Resetting A Car Computer With An OBD2 Scanner

This method will be perfect for resetting the car’s computer after replacing the battery. With this method, you can be sure that your computer is reset and all the check engine lights or other errors are removed from your system. This will result in no check engine light on the dash and a perfectly working car. So, how you can do this?

To do this practice, you will need a diagnostics tool. Also called an OBD2 scanner. You can find these scanners for a cheap price online and they are readily available. A good OBD2 scanner will cost you more money. But it’s worth it. The more options the scanner has, the more easily it will be for you to diagnose an issue. Since most cheap scanners only show you the error codes and you have to look for them online.

The best tools are the ones that can connect to your mobile phone and have a mobile app. With this app, you will have no trouble resetting your car’s computer after replacing the battery.

You only need to connect the tool to your OBD2 port. This port is usually located under the steering wheel. Then you open the app and let the app scan for codes. If there are any codes on your computer, the app will show them to you and you will have the option to erase them altogether from your system.

Once erased, turn off your car and then restart the car. Scan the car again with the tool. If the error still persists this means that you have a bigger issue. Make sure that you read the codes and learn more about them and troubleshoot the issue. Here is a video of how this work is done.

3. Take Your Car To Be Diagnosed By A Mechanic

The last way to get this done is at a shop. There are shops that are doing full diagnostics and this will cost you some money to get your car diagnosed and the reset car computer after replacing the battery possible.

This service is going to cost you somewhere between $50 to $150 to get all the codes deleted and removed from your system. But this doesn’t mean that they will not return again. But if the check engine lights a false positive from a battery replacement it should be gone.

4. Fuse Removal Method

Another method that sometimes works is the fuse removal method. This doesn’t involve completely disconnecting the battery but does require a bit more knowledge about your car’s fuse box.

First, find your car’s fuse box. It is typically located under the hood or dashboard. Once you’ve located the fuse box, look for the Electronic Control Unit (ECU) or Engine Control Module (ECM) fuse. This might differ from car to car, so checking the car manual is beneficial.

After identifying the correct fuse, pull it out using a pair of needle-nose pliers or a special fuse puller tool. Wait for about 10 minutes and then reinsert the fuse.

Turn on your car, and the computer should be reset. This method not only resets the ECU but also any temporary memory glitches in other systems, possibly caused by a battery change.

5. Brake Pedal Method

This might sound unconventional, but some drivers swear by this method. Here’s how you do it:

With the car, ignition turned off, press and hold down the brake pedal. While holding the brake pedal, disconnect the battery’s negative terminal. Keep pressing the brake pedal for a minute or so.

This action drains the remaining electrical charge in your car’s systems, including the ECU. Now, reconnect the battery terminal and release the brake pedal. When you turn on the car, the ECU should be reset.

6. Full-Drain Method

This method is an extension of the first one but guarantees a complete electrical drain, ensuring the car’s computer gets fully reset.

After disconnecting the positive terminal, also disconnect the negative terminal. Then, touch both the battery cables together for about 3 minutes. This will drain any residual power from the car’s systems.

Once done, reconnect the terminals starting with the positive first. This method ensures a complete system reset.

7. Wait and Drive

Sometimes, the simplest approach is to just wait. Modern cars are equipped with self-adaptive ECUs that learn and adjust over time. After replacing the battery, the ECU might need some time to recalibrate.

To expedite this, consider driving your car under various conditions over the next week or so. This includes highway driving, city driving, and even some idle time. This real-world data helps the ECU adapt and optimize for current conditions.

8. Disconnecting Specific Sensors

In some cases, disconnecting specific sensors, like the mass airflow sensor, and then turning on the ignition (without starting the car) can reset the ECU. Remember, this method isn’t universally applicable, and you should consult your car’s manual before trying.

After following any of the methods, it’s advisable to check your car for any system-specific codes. If anything unusual pops up, it’s always a good idea to consult with a professional.

In conclusion, there are multiple methods to reset a car’s computer. The right method for you depends on your comfort level with car mechanics and the tools available. Remember, when in doubt, consulting a professional is always the best course of action.

Car Computer Reset Cost

Resetting the computer of your car if you only remove the positive terminal on your battery will cost you 0 dollars and you can do this work at your home with no previous car knowledge.

The next way is to take your car to a shop. Let the mechanics do this work on your car and remove all the codes. This will cost you somewhere between $50 to $150. This way is perfect for people who don’t want to mess with their cars and just want their problems out of their lives.

The third way is to do it by yourself. Get an OBD2 scanner tool, if you get one that you could connect with a mobile phone would be perfect. Since these tools tell you a lot more than the cheap $30 scanners. This tool can be pricier and you could pay around $100 or more for this tool.

Scan the car for codes and remove them. This will reset all of the settings. If the check engine light still persists and you experience some problems with the overall engine operation and the car is in perfect mechanical order. Maybe the ECU is somewhat broken. The worst symptoms that you can feel as we said are the car not starting or shut down all of sudden. In this case, you know that you have a problem.

Reset Car Computer After Replacing Battery: In Conclusion…

In this article, we have covered a lot when it comes to check engine light problems concerning the car battery. We learned what is a car battery and how it works. Then we learned what is the ECU and how the ECU is controlling all the systems in your car.

Then we have covered all of the symptoms of a broken ECU since one of the problems of this unit is when it breaks it sends check engine lights on the dashboard for no particular reason. Like in our example, you install a new battery and you get a check engine light. Something that doesn’t make sense.

Then we learned how you can get rid of the check engine light and how to reset the computer. There is the removal of the power supply method. Which involves removing the positive cable from the terminal. Then take your car to a diagnostics shop and the last method is to reset a car computer after replacing the battery by yourself using an OBD2 scanner tool. Any way works, it depends on you how you want to tackle the problem.

Reset Car Computer After Replacing Battery Essential Knowledge

  1. Cars manufactured since the 1970s have onboard electronics, including the Engine Control Unit (ECU) and vehicle diagnostics systems.
  2. The ECU reads sensors and controls specific elements of the engine to provide optimal performance.
  3. Disconnecting the car battery should not cause permanent damage to the ECU if the correct procedure is followed.
  4. Disconnecting the battery may cause the ECU to forget some settings and data points, such as preset radio stations or ideal shift points.
  5. A full reset of the ECU reverts it to its factory settings and may cause rougher acceleration and shifting than usual.
  6. The ECU will eventually relearn its ideal settings and reprogram itself with use.
  7. It is important to follow proper safety procedures when disconnecting and replacing a car battery.
  8. Disconnecting the battery and draining power can be a fix for a check engine light that won’t go away on its own.
  9. If the check engine light comes on again after resetting the ECU, the car might have a severe issue.
  10. If you have an OBD-II scanner, you can check for engine trouble codes yourself by locating the car’s OBD-II port, plugging in the scanner, and checking for active trouble codes.

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Melody Salvo 03/02/2023 - 2:05 am

I have tried multiple ways to reset the security system and none of them work. We have disconnected the battery and the only light that remains on is the security system light. How do I reset it or turn it off?

Paul Hadley 07/25/2023 - 4:28 pm

I understand your frustration, Melody. Dealing with a persistent security system light can be quite challenging. While disconnecting the battery is a common method to reset the car’s computer, it seems like it hasn’t resolved the issue in your case.

In situations like these, it might be best to consult the car’s manufacturer or a professional mechanic who specializes in your specific make and model. They would have the expertise and knowledge to diagnose the problem accurately and provide you with the correct steps to reset or turn off the security system.

It’s important to remember that each car’s security system may have different reset procedures, and what works for one model may not work for another. Seeking expert advice will ensure that you receive the most accurate and tailored solution for your particular situation.

I hope this helps, and I wish you the best of luck in resolving the issue with your security system light.

Paul Hadley 07/25/2023 - 4:41 pm

It seems like you have been facing some difficulties with resetting the security system after replacing the battery in your car, Melody Salvo. I understand how frustrating this situation can be. Disconnecting the battery is usually an effective method to reset the car’s computer, but it seems that the security system light is still illuminated.

In such cases, it might be helpful to consult your car’s user manual or contact the manufacturer’s customer support for specific instructions on resetting the security system. They would have the most accurate information and can guide you through the process step by step.

If you have already attempted various methods without success, it’s possible that there could be an underlying issue with the security system itself. In this case, it might be advisable to have a professional mechanic or an authorized service center take a look at your car. They will have the necessary expertise and equipment to diagnose and resolve any security system-related problems.

Remember, it’s essential to ensure the security system is functioning correctly for the safety of your vehicle. By reaching out to the manufacturer or seeking professional help, you can hopefully find a resolution to this issue and have your security system reset or turned off.


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