Will Disconnecting the Car Battery Harm the Computer?

There are many reasons you might need to disconnect your car's battery, but will it somehow damage your car's computer? To help you answer that question, we have researched all of the best resources to find out how to perform this procedure and what kinds of negative consequences it can have on your car's computer. This will allow you to decide if it is worth the trouble, or if pursuing another route is better for your situation.

Disconnecting your car battery will not cause any permanent damage to your computer or ECU (electronic control unit), but it can have some adverse effects. Those include canceling your preset radio stations, forgetting learned shift points, and your car's ideal fuel/air mixture. Depending on your vehicle and its anti-theft system, it may also lock you out of the car.

But wait, there's a lot more to know about your car battery and computer, so stay with us. In this article, we will discuss the correct procedure to follow anytime you disconnect the battery. We will also discuss how to reset the computer without going through all of that trouble.

Last, but not least - this post is for entertainment and educational purposes only. We want to help you understand what your mechanic is doing - not try to replace her or him.  if you don't have the appropriate background, you should not try this at home. Not only would you be putting your vehicle at risk - but also put yourself at risk. 

From this point on, where we say "you" imagine it's your mechanic there! 

A mechanic disconnecting the car battery terminal

Will Disconnecting a Car Battery Harm The Computer?

While disconnecting the battery will not permanently damage your vehicle's computer, it can cause it to function differently. That's because, if you disconnect your battery for long enough to reset the computer, it may cause the processor to forget everything it has learned.

That's right, your computer learns as you drive - where the best places to shift are, how you like to accelerate, and even how to best mix fuel and air to create combustion inside the engine.

Leaving the ECU without power for a significant amount of time (over 5 - 10 minutes) will likely cause it to reset back to square one. This means it will have to re-learn all of those things. Because of that, your car won't run like you are used to - the engine may run a bit rougher, and the acceleration and shifts might seem "off" as well.

Some cars even require you to use a scanner to input battery information before the computer functions. These vehicles are programmed to adjust to the battery's charge rate, so giving it your battery's data will allow it to charge the battery correctly as it ages.

Will Disconnecting a Car Battery Reset The Computer?

Male car mechanic doing chip tuning and service with car computer

The answer is, maybe. Disconnecting the battery for a short time may not do the trick because the car's computer, or ECU, still has some current in it. Waiting for over 15 minutes after disconnecting the engine will help ensure the equipment is reset.

How To Reset Your Car Computer Without Disconnecting The Battery

While disconnecting the battery is the most common method of resetting your computer, it's not always the best way. That's because disconnecting the car battery causes your computer to lose its memory. So, things like your preset radio stations, shift points, and your car's ideal fuel/air mixture are forgotten. Also, your anti-theft system may lock you out of the vehicle.

If you need to reset your computer without disconnecting the battery, there is likely a precise series of steps you must follow. This procedure is different for every vehicle, however, so you might have to do some googling or look in your owner's manual to find the correct process for your needs.

Here are the steps for some of the most popular vehicles.

Ford F150

2020 Red Ford F-150 Raptor pickup truck at a Ford dealership

Because it is the most popular model on sale today, we will start with the Ford F150. Note, however, that ">this procedure will work for many other Ford models, including Super Duties and Explorers, as well.

Again, keep yourself and your truck safe, and do not try this at home unless you're sure you know what you're doing. This is just to show you what a professional will likely be doing. 

  1. Disconnect the negative terminal
  2. Place a rag or something non-conductive over the negative terminal
  3. Connect one end of a jumper wire (like this one on Amazon) to the positive terminal (which is still attached to the battery)
  4. Connect the other end of the wire to the un-attached negative cable, making sure it doesn't come into contact with the battery terminal
  5. Wait for 5 - 10 minutes, then disconnect the cord
  6. Reconnect the negative cable
  7. Turn on the ignition and idle the engine for 5 to 10 minutes. This allows the engine to learn the idle values - turn off all accessories during this time.
  8. Take your vehicle on a test drive to allow it to learn shift points - make sure to hit each gear in your car using light acceleration

Honda CR-V

A stunning red Honda CRV display during motorshow

Another super popular vehicle is the Honda CR-V crossover. Here is the process for resetting the computer:

  1. Open the fuse box (located under the hood)
  2. Remove the box's cover by opening the tabs and lifting the top off
  3. Using a fuse tool or needle-nose pliers, pull out the 7.5A fuse (labeled"Back-Up") and the 15A fuse (labeled "ECU")
  4. After about 10 minutes, plug the fuses back in
  5. Start your vehicle, let it idle for a few minutes, then take it for a test drive to check that it worked

Toyota Camry

Black Toyota Camry display during motorshow

While it is not the sales leader it once was, there are still tons of Camrys on the road. Here is the procedure for resetting the ECU (to be done in the safety of a proper vehicle garage by a pro):

  1. Find the fuse panel located under the steering column
  2. Pull down to open it
  3. Using the included fuse diagram, locate the fuse for the ECU (electronic control unit)
  4. Using the fuse puller included inside the fuse box, pull out the ECU fuse
  5. Put your key into the ignition and turn the car on (without starting it)
  6. After a few minutes, re-install the ECU fuse
  7. Test your process by idling and then test-driving your Camry

How Do You Safely Disconnect a Car Battery?

Auto mechanic replacing a car battery

If you decide that you need to disconnect your battery, there is a right way and a wrong way to go about it. It is essential to get it right, both for your safety and that of your vehicle. First off, you will need to make sure you have the right tools to complete this job safely and correctly:

Items needed

Please remember that this post is for educational purposes only. If you've never done any mechanical work on a car before, you should take your car in to be seen by a mechanic. 

Consider this as a list of gear that shows you what a professional would need to disconnect a battery.

Safety goggles

Pair of safety goggles

Always protect your eyes when working with any tools or machinery. A pair of inexpensive safety glasses can save you a lot of money during ER visits. Not to mention saving your eyes.

Click to see this pack of safety glasses on Amazon


Electrician working in a residential electrical system

When working with electric appliances, the right pair of gloves can protect more than just your skin. High-voltage safety gloves can insulate you from a dangerous surge. Never rely just on gloves or any other protective gear, though. Some jobs are just best left to professionals.

Check out these safety gloves on Amazon 

Socket wrench

Ensure you own the correct-sized socket for your battery terminals (and an extender might be necessary, depending on your wrench and your car).

Open drawer of tools in real life workshop

Prepare Your Car and Yourself

Before you begin, it's essential to make the right preparations for the task at hand. This isn't all that hard - turn off the ignition and put on some gloves and safety goggles.

Remove the Negative Terminal

The most important thing to remember is this; you must always remove the cable attached to the negative terminal first. Now, locating the negative terminal is easy. Terminals are the point where the wires from your engine connect to the battery - the negative one is always under a black cover. It usually has a minus sign next to it, as well.

Using a socket wrench, loosen the nut holding the cable clamp onto the battery terminal, then slip the cable off. Just a few turns should be plenty to get the clamp loose enough. Once the cable is removed, be sure to place it somewhere so that it will not come into contact with the battery during the rest of the process. Placing a rag over the terminal will ensure that the cable doesn't swing around and make contact with it.

Remove the Positive Terminal

Now it's time to take the cable off of the positive terminal. If you haven't guessed yet, this is the red terminal on the opposite side from the negative (black) terminal.

Follow the same procedure as in the previous step to get the positive cable removed. Once it is off the battery, it is essential not to let the positive cable contact any metal in the engine bay. At this point, your battery is disconnected, and you are free to continue with whatever job you are working on.

What Happens If You Disconnect The Positive Terminal First?

Positive battery terminals in the car's engine compartment

So, why is it so important for your mechanic to follow the above steps to disconnect the battery? First, let's understand what those terminals actually do and why they are labeled differently.

The positive terminal connects to everything in your vehicle that uses electrical power. Meanwhile, the black terminal is connected to a couple of bolts inside the engine bay. Connecting the two terminals runs a current of electricity through whatever lies in between them, as long as this item conducts electricity.

Because the negative (black) cable is attached to a metal surface inside the vehicle, the positive (red) wire will complete the circuit by touching just about any unpainted metal surface on the car. The electric current can even jump between the cable and a nearby metal surface. This can easily result in a nasty shock or even a fire. Fortunately, this scenario is easily avoided by disconnecting the power to that negative terminal first.

Does Disconnecting Battery Reset Check Engine Light?

Yellow engine check engine icon on car dashboard

Yes, disconnecting the engine is one method of resetting your check engine light. Because some of the electrical current is preserved in the computer for a while afterward, most sources recommend leaving the battery disconnected for at least 15 minutes to make sure the computer forgets the code before you reconnect the battery.

Other experts recommend turning on the light switch for a few minutes (the lights won't come on) after disconnecting the engine to drain any remaining current on the computer.

Remember, before you go this route, that this method of resetting your check engine light has some negative consequences as well. If you would rather not deal with those, note that you can also use an OBD2 scanner tool to reset these fault codes if your vehicle was built after 1996, and you have access to one of these tools like this one for sale on Amazon.

Knowing how to care for and maintain your vehicle is a rewarding skill, and it is never too late to start! We appreciate that you took the time to learn the ins and outs of disconnecting your battery. No matter the reason you need to disconnect it, be sure to get the help of a professional to keep you and your possessions safe.

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    • Thanks for the comment, Regina. A simple Google search indicates that VCM = Variable Cylinder Management = Honda’s variable displacement technology that helps conserve fuel. Is it possible you’ve confused something on your vehicle with that term?

  1. I hv a 2006 300c before I had plugs put in it it ran good check engine light was told them to check and see way d light is on n went n pick up my car it starts put in drive it cut off n they kept it for 2 days n call me n told me that d computer was bad need another computer but before I had plug put in had no problem with it stay running so do I need another computer are do it need to b reset

    • Melvin, our recommendation is to have your vehicle inspected by a certified and reputable mechanic for further diagnosis.

  2. i have a 2005 ford expedition all the gauges worked before i put a fuel pressure sensor which on this model with a 5.4 Triton v8 is on the fuel rail now i have owned a repair garage and two used carlots for 21years so i do have experience after replacing the bad sensor the fuel gauge no longer works. Any tips at this point i want to pull engine and transmission out of it and buy two other expedition trucks in the tow row at the auctions and use this one for parts too bad this one now runs perfectly only 101242miles but ive never came across this problem before. i scanned it before and that was the issue i drove it 54 miles scanned it again and no codes come up as well as no check engine light and it now runs perfectly fine please if someone knows why the gas gauge stopped working please respond

  3. when you reset the ecu it has to learn, its good to turn key ON for 30 seconds then OFF, ON again and then START ENGINE accelerate a few times and let the engine to warm up, when warm accelerate a few times and open all lights wipers etc to let the ecu read power consumption, den drive the car a few blocks

  4. Having a problem with a 2019 Explorer. Battery went DEAD! NO WARNING and a year old???? Come on Ford!!! Got new battery and now the terrain drive won’t change manually AND it makes a JERK in the car; a light comes on that the terrain drive is malfunctioning… NOW an open wrench / 2 ended shows and I am afraid to drive the car. HOW do you get to the dealership to have it checked IF #1 the battery is dead and #2 the transmission/ terrain drive is acting up? HELP!!! PLEASE!

  5. I have a 2012 chevy malibu 2.4 6 speed lt model. I noticed my car throwing codes for not recognizing the passenger side serial info. Now I am getting can bus no communication codes. The other day my car wouldn’t start. I put the key in and turned it and I could turn it to on but the moment I went past on all the electricity turned off and it didn’t crank, no furmel pump was ever heard. The issue seamed to go away all on its own. When I had tried to start it and it just started put of nowhere. Now it happened again the other day. And went away the next day was fine. I do know that the car’s battery was disconnected when the key was in the on position, not running , just on. I think it messed up my pcm or ecu. Is that what happened? And if so. Can it be reprogrammed or do I need to buy a new one?
    Thank, faith

  6. So if I ever do work on my car, that requires me to disconnect the battery, what’s the best route to take to keep my car running like before? I replaced my spark plugs in my 2012 mustang and my cold air intake is hot. What would a ford mechanic do if I took it to one.

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