How Long Should You Disconnect Battery to Reset ECU. 12v battery reset

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!

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?

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

Because it is the most popular model on sale today, we will start with the Ford F150. Note, however, that 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.

  • Disconnect the negative terminal
  • Place a rag or something non-conductive over the negative terminal
  • Connect one end of a jumper wire (like this one on Amazon) to the positive terminal (which is still attached to the battery)
  • 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
  • Wait for 5. 10 minutes, then disconnect the cord
  • Reconnect the negative cable
  • 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.
  • 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

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

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

Toyota Camry

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):

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

How Do You Safely Disconnect 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

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.


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.

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).

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?

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?

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.

long, disconnect, battery, reset

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.

Thursday 10th of November 2022

How Long Should You Disconnect Battery to Reset ECU?

Everyone who drives has experienced the dreaded check engine light. You take your car to the mechanic who says nothing is wrong with your car. Great, you think. Now what?

You could pay for a full vehicle diagnostic, but you could also try resetting your car’s ECU.

To figure out if you need an ECU reset, we’ll define what an ECU is, what resetting an ECU can and cannot achieve, and teach you how to reset your ECU.

Understanding an ECU Reset

To understand what an ECU reset is, we must understand what an ECU is. An ECU, or engine control unit, is a piece of electronic equipment present in most cars and trucks that controls the engine’s actuators. An ECU reset recalibrates your engine control unit by wiping its memory of your engine’s performance.

Why Do You Need an ECU Reset?

For example, resetting an ECU can be used to reset an engine’s optimum idling RPMs. Your car’s computer may need to be replaced if your engine idle improves after an ECU reset. In contrast, an ECU reset that results in a rough engine idle may indicate a mechanical problem.

You can also use an ECU reset to reset faulty check engine lights or other dashboard warnings. Faulty dashboard lights can cause your vehicle to fail its yearly safety inspection. By resetting your vehicle’s ECU, you effectively erase the computer’s memory of any issues your car engine was experiencing. Be aware that resetting your ECU is not a permanent solution to faulty check engine lights, but it may help you pass a vehicle inspection.

How Long Do You Leave a Battery Disconnected to Reset ECU?

You should leave your car’s battery disconnected for a minimum of fifteen minutes and no longer than thirty minutes to reset an ECU. To disconnect a car battery, remove the negative power cable from the negative terminal of your car battery with the use of a socket or monkey wrench.

Does Unplugging a Car’s Battery Reset the ECU?

Unplugging a car’s battery will reset the ECU in older vehicles—makes from about 1980 to 2005. Newer vehicles use computers with more advanced memory systems that store engine information even when the computer is disconnected from power.

Do You Have To Disconnect Both Battery Terminals to Reset ECU?

You do not have to disconnect both of your car battery terminals to reset an ECU.

You may choose to disconnect both battery terminals to reset an ECU, but it is not required. All you need to do to reset your ECU is interrupt the power flow from the car battery to the car’s ECU. The most efficient way to disrupt the ECU’s power supply is to disconnect the negative cable from the negative terminal.

What Happens if You Disconnect the Positive Terminal First?

You must disconnect the negative terminal of your car battery first if you plan to reset your car’s ECU by disconnecting the battery.

Disconnecting the positive terminal of a car battery while the negative terminal is still connected can lead to battery arcing. Battery arcing is a dangerous condition where an electric current jumps a gap in a circuit. An arc can cause a powerful charge to be transferred from the car battery to other metal parts of your car, leading to hazardous sparks.

How to Disconnect a Battery to Reset ECU?

Resetting an ECU by disconnecting a car battery is a simple process that anyone can do. Please be aware that resetting an ECU usually takes anywhere from 30 minutes to an hour, so plan accordingly.

ECU Reset Tools Needed

You will need a socket or monkey wrench, a set of jumper cables, a rag or piece of cloth, and your car keys to reset your car’s ECU by disconnecting the car’s battery. Optional: gloves to prevent your hands from getting dirty.

Step 1

Locate your car’s battery. Disconnect the battery’s negative cable from the negative terminal using your preferred wrench. Isolate the negative terminal by placing a rag or piece of cloth between the battery terminal and the negative cable.

Note: the negative terminal is denoted with a minus (-) symbol and is usually color-coded in black.

Step 2

Take your jumper cable and connect one of its clamps to the isolated negative cable. Take your jumper cable’s other clamp and connect it to the positive terminal. Once the circuit is complete, wait for at least 15 minutes.

Step 3

After 15 minutes (or more) have elapsed, disconnect your jumper cables from the car battery. Reconnect your car’s negative power cable to the negative terminal of the car battery.

Step 4

Insert your car’s key into the ignition. Turn the ignition key until the car’s dashboard lights come on, but do not turn the engine over.

Note: When done correctly, the fuel gauge needles and dashboard lights of your car will activate, but the engine will not turn over.

long, disconnect, battery, reset

Now turn the ignition key back to its starting position to turn the car off. Now turn the car back on, this time turning the engine over.

Let the car idle for fifteen minutes. Your car’s ECU is now reset and will recalibrate after driving a few hundred miles.

How Long Does It Take for a Car Computer to Reset?

The process to reset a car’s computer takes about an hour. Once a car’s computer has been reset, it will take a few hundred miles of driving for an ECU to rerecord the vitals of a car engine.

Can You Reset a Car ECU Without Disconnecting the Battery?

You can reset your car’s ECU without disconnecting your car battery.

The purpose of disconnecting a car battery is to remove an ECU’s power supply. ECUs, especially on older vehicles, are designed to reset after they have lost their power source. Removing the ECU fuse from your vehicle’s fusebox will achieve the same result as disconnecting your car battery: it will interrupt the ECU’s power supply.

How to Reset A Car ECU Without Disconnecting the Battery

First, make sure your car is off. Then locate your car’s fuse box. Fusebox locations vary between car makes and models, but most are located on the driver’s side of the car. Refer to your vehicle’s owner manual to expedite the location of your car’s fusebox.

Once you have located your car’s fusebox, remove its protective panel. Locate the fuse labeled ECU (In some vehicles, the fuse may be labeled ECM). After 15 minutes have elapsed, replace the ECU fuse and restart your car.

Author: Dave Johnston

Dave Junior is a hands-on automotive technician with experience in performing service, diagnostics, and repairs on domestic and imported vehicles. He enjoys writing and sharing his knowledge far and wide.

How To Reboot Your Car ~ Battery VooDoo

Modern cars are basically rolling computer storage. As with all computers, vehicle computers get fussy from time to time. A computer acting fussy can lead to strange electrical problems in our cars. One easy way to reset the entire car system is to perform battery voodoo. In the VW repair world this is also called a Cap Discharge, or Capacitive Discharge. That is a fine thing to call it, but it’s not exactly what we are doing.

This hard reset on the car has fixed a lot of strange issues for me. Everything from radio and lighting issues, to gauges reading funny, and electrical components not working. This is a relatively safe process, but you will always want to take extra precautions to keep yourself safe and not damage your car.

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Kia Optima Hybrid: Charging System / Auxiliary 12V Battery Repair procedures

Install the battery upper bracket after locating the battery at the closest position to the side panel.

For an accurate measurement of a vehicle parasitic current, all electrical systems should go to sleep mode. (It takes at least one hour or at most one day.) However, an approximate vehicle parasitic current can be measured after 10~20 minutes.

Connect an ammeter in series between the battery (-) terminal and the ground cable, and then disconnect the clamp from the battery (-) terminal slowly.

Be careful that the lead wires of an ammeter do not come off from the battery (-) terminal and the ground cable to prevent the battery from being reset. In case the battery is reset, connect the battery cable again, and then start the engine or turn the ignition switch ON for more than 10 sec. Repeat the procedure from No. 1.

If the parasitic current is over the limit value, search for abnormal circuit by removing a fuse one by one and checking the parasitic current.

Reconnect the suspected parasitic current draw circuit fuse only and search for suspected unit by removing a component connected with the circuit one by one until the parasitic draw drops below limit value.

Care should be taken in the event the battery case is cracked or leaking, to protect your skin from the electrolyte.

Inspect the battery tray for damage caused by the loss of electrolyte. If acid damage is present, it will be necessary to clean the area with a solution of clean warm water and baking soda. Scrub the area with a stiff brush and wipe off with a cloth moistened with baking soda and water.

Clean the inside surface of the terminal clamps with a suitable battery cleaning tool. Replace damaged or frayed cables and broken terminal clamps.

Connect the cable terminals to the battery post, making sure tops of the terminals are flush with the tops of the posts.

When batteries are being charged, an explosive gas forms beneath the cover of each cell. Do not smoke near batteries being charged or which have recently been charged. Do not break live circuit at the terminals of batteries being charged.

Auxiliary 12V Battery Description and Operation

Description 1. The maintenance-free battery is, as the name implies, totally maintenance free and has no removable battery cell caps. 2. Water never needs to be added to the maintenance-free battery. 3

Cruise Control System

Other information:

Kia Optima Hybrid (TF HEV) 2016-2020 Service Manual: NVLD(Natural Vacuum Leakage Detection) Description and Operation

Description NVLD(Natural Vacuum Leakage Detection) is located between the canister and the fuel tank air filter. NVLD is to detect leaks equivalent to a 0.5 mm hole in the fuel tank, canister and hoses. When the engine has been running, the temperature of the fuel in the fuel tank is raised slightly

Kia Optima Hybrid (TF HEV) 2016-2020 Service Manual: Curtain Airbag (CAB) Module Description and Operation

Description Curtain airbags are installed inside the headliner (LH and RH) and protect the driver and passenger from danger when side crash occurs. The SRSCM determines deployment of curtain airbag by using side impact sensor (SIS) signal. Never attempt to measure the circuit resistance.

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