Does Disconnecting Battery Reset ECU? Best Answer and Fix! (2023)

ECU (Engine Control Unit) takes charge of sustaining a strong and consistent combustion engine performance.

Hence, any unexpected problem with the motor compartments calls for a thorough ECU reset.

But still, how to reset ECUs and what would wipe off their board memory remains a mystery for many novices. So does disconnecting battery reset ECU? Will it bring about any harm to the car?

Our guides will delve further into the question, Can disconnecting battery reset ECU? Keep scrolling to pick up the answer you need!

Why Are ECU Resets Necessary?

Does Disconnecting Battery Reset ECU? Best Answer and Fix! (1)

ECUs resets help you diagnose control unit malfunctions, address severe engine misfires, and fix your faulty check engine lights.

Let’s say your optimum RPMs suffer through technical issues; ECU resets can serve as an antidote to revive its original state.

Broken engine lights or other expected dashboard warnings can also be tackled this way.

Once the ECU resets itself, any computer memory related to the issues will be wiped off entirely, sending your car back to normal.

By no means should it be considered a permanent resolution. But at the very least, you can still run the cars safely for a while before having time to visit a mechanic.

Does Disconnecting Battery Reset ECU?

Will disconnecting battery reset ECU? It’s difficult to confirm a definitive Yes or No. Not all cars are the same, which means ECUs will respond variedly based on the model and make of your vehicle.

Also, if the problem lies within the ECU fuse box itself, then the battery disconnect will not be as straightforward.

Overall, basic and simple steps are available to achieve a true reset without issues. One approach is to disconnect your batteries for a period of time (5 – 10 minutes).

(Video) Toyota / Lexus Rough Idle After Battery Change/Disconnect - Idle Reset Relearn Procedure

Another is to disjoin them and start the engine almost immediately – which will do for most older vehicles.

But again, remember that we cannot guarantee whether either method is ALWAYS effective; thousands of car designs render one-size-fits-all solutions impossible.

There are cases where both approaches do not work at all.

Under severe circumstances, it would be best to simply bring the car to professional mechanics and ask them for further inspection.

On another note, resets might fail if the electronic control unit itself undergoes problems – or your car suffers from any other errors you are unaware of. Again, contact a mechanic service to make sure.

How Long Will It Take For The Cars’ ECU to Relearn?

Average calculations fall into 500 miles or thereabouts.

Still, here are some tips to speed up this process: driving the car in varied conditions, turning to professional services for ECUs, and leaving the car fully idle for ten minutes.

An exact estimation is not feasible since numerous factors play a part; cases in point include the ECU type, changes your engine bay has received, and driving habits.

But overall, relearning often takes about 500-550 miles.

After all, the unit must collect 100% sensor data (O2 sensors and cam sensors) within the steering column, ignition switch, and fuel injectors. And trust us, that is not an immediate process!

But who says you cannot speed things up a bit? There are still certain tricks up our sleeves. Driving the vehicle in different conditions (city, highway, etc.) will make it learn much faster.

A professional tuning service for ECUs might also help, as these mechanics own a broad range of special software and tools quite rare in most retail stores.

Such devices generate faster electrical power loss and foster instant ECU reset.

(Video) Here’s Why Disconnecting Your Battery Will Destroy Your Car

In another vein, one suggested solution by experts is to leave the vehicle idle for about ten minutes.

Such approaches give sufficient time for your control unit to optimize the car’s performance and absorb new information. Real engine issues will also be kept at bay.

Negative Battery Terminal versus Positive Battery Terminal: Which One Should I Disconnect First?

Do I disconnect the positive or negative to reset ECU? We suggest you disconnect negative battery terminal to reset computer.

Reverse orders will produce a harmful spark that leaves behind permanent damage.

First, pick up a high-quality combination wrench and loosen the negative cable clamp. Slide it off your battery post, before doing the same with your positive cable.

(for more detailed guidelines, please refer to the next section)

When Do Your ECUs Need Resetting? Some Common Symptoms

Anything unusual with the engine warrants ECUs resetting. Some common symptoms include engine rough running, stalling, and hesitating (Worse, certain situations even witness all three!).

Postponements will only worsen the issue beyond saving; thus, you must reset ECU by disconnecting battery as quickly as possible.

Disconnecting Battery to Reset ECU: Step-By-Step Instruction

Wear gloves/goggles and switch off the ignition before you start. Spot the negative battery terminal (with a minus symbol) and disconnect its connector.

Do the same with its positive terminal. Once all terminals are detached, proceed with whatever repairs your car needs.

Step 1. Take some safety cautions before you start, as batteries include corrosive elements that produce flammable gas. Do not forget to switch off the car’s ignition and wear safety gear (gloves/goggles) to cover your hands and eyes.

Step 2. Identify the battery’s negative terminal, which is often covered in black with one minus sign next to a connector post. Positive terminals, on the other hand, have red caps with plus signs.

Step 3. Assess the appropriate size socket to slacken the terminal’s nut. Again, tackle the negative terminals first before moving on to their positive counterparts.

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Hold the socket near – not against – the nuts. Once you have ascertained the right size, put the socket on your wrenches. In some cases, you might need to use wrench extenders to reach for the nut.

Step 4. Insert the wrench and turn it counterclockwise. After two to three turns, the nut will slide off. Then pull out the battery’s negative connector and gently put it far from your working area. That way, these cables will not be able to touch the battery.

But what if the wrench fails to remove the connector? Maybe a special tool for cable removal will do better, which you can purchase at local stores.

Step 5. Repeat these steps to the battery’s positive terminal. Never let the positive connectors touch any metal, as their residual currents might interrupt (or worse, damage) the vehicle’s circuits.

Step 6. Go on with your repair. Now that all battery cables are disconnected, it’s possible to safely apply necessary repairs to the car’s electrical components.

How to Perform ECUs Resets Without Disconnecting Batteries

Remove the fuses from their box and wait 10-15 mins before inserting them back.

Once done, test how the car operates on the street: smooth acceleration pedal and non-blinking engine lights mean all is well!

So what if resetting ECU by disconnecting battery terminals sound unappealing to you?

Then one alternative is to disjoin their fuse cover instead, which also causes power loss – and subsequently, an ECU reset.

One huge downside, though, is that you need to identify which fuse takes charge of the ECUs. And here is bad news: it’s quite tough to find! Still want to give it a try? Then follow our guidelines:

Step 1. Open The Hood to Remove The Fuses

Once the vehicle hood opens, its fuse box will get revealed, located behind the car’s engine. Identify all fuses labeled “Backup” and “EMU/ECM” and extract them all.

Step 2. Wait For Some Time Before Reinstalling Them

There’s no need to uninstall these fuses too long. About ten to fifteen minutes will be sufficient.

Do not leave their covers behind, as your fuses will be prone to damage without proper protection.

(Video) How To Reboot Your Car ~ Battery VooDoo

Step 3. Test How The Car Runs

Granted you followed our instructions with great care, your computer resets have achieved massive success!

Drive the car a few miles to inspect how it operates, keeping a close eye on its road behaviors and engine lights (which should be turned off by now).

Blinking engine lights, on the other hand, indicate a severe fuel issue and require more specialized support!


1. Do Disconnected Batteries Help Clear Error Codes?

Yes, obviously. Any notable fault code will be erased, switching your control unit to its entry-level state.

2. How Long Does It Take Me to Reset BMW ECUs?

Most BMW cars call for about 15 minutes. Sometimes the process might need more time than that – but it never exceeds 30 minutes.

Still, not all manual transmission issues in BMWs call for ECU resets. The causes behind these dilemmas are sometimes simpler than we think, so resetting ECUs is the last resort if all other solutions fail you!

Also, note that there are differences between BMW check engine lights and BMW service engine soon lights – and the latter does not necessarily require ECUs resets, either.

3. How Long Do Car ECUs Last?

Unless there are unresolved issues, ECUs are supposed to last as long as your vehicle does. The precise number fluctuates across different car models.


Does Disconnecting Battery Reset ECU? Best Answer and Fix! (2)

Does disconnecting battery reset ECU? Our article has discussed this issue and more.

Different approaches – both with and without battery connections – are introduced, so feel free to choose one that suits you best.

Most importantly, always wear safety gear to avoid mishaps!For more questions on how to reset car ECU with battery, feel free to contact Bryan’s Garage.


Does disconnecting the battery reset the ECU? ›

Disconnecting your battery and draining the power to cause an ECU reset is one of the most common fixes for a check engine light that won't go away on its own. Doing so is equivalent to a hard reboot on a desktop computer, which is a standard way to eliminate many common problems.

Will resetting an ECU fix it? ›

Resetting your ECU is a popular myth. In reality, resetting your engine control unit (ECU) after modifying your engine isn't necessary. However, resetting your ECU can help you fix a faulty check engine light.

How long does it take for ECU to reset after disconnecting battery? ›

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.

Will disconnecting car battery reset everything? ›

On some older cars, disconnecting the battery will reset the system but in most new cars it does nothing, except potentially reset the clock and radio station presets.

How many miles do you have to drive to reset ECU? ›

Here's something you probably don't know: after clearing the car's computer you will need to drive for about 50 to 100 miles. As you drive your car the computer will monitor all the sensors and register the results.

Does replacing the car battery reset the ECU? ›

Most ECUs are self-learning and should reset themselves after learning that a new battery has been installed. If you're stuck, go to a mechanic for diagnostic assistance.

What is the purpose of ECU reset? ›

The main purpose of ECU reset is to recover the malfunction or not working condition or ECU hanged state, but it should able to communicate the external diagnostic system. At this point of time ECU/Server does not receive any request messages and also not respond to any messages.

What will happen if I reset my ECU? ›

"Resetting the ECU" is the process of clearing all the long term memory from the ECU's memory. These variables trim idle speed, fuel, spark, and more. The ECU will also store trouble codes for diagnostic capability.

Which battery cable do I disconnect to reset computer? ›

Use a wrench to loosen the negative terminal bolt, and then take the negative cable and hold it aside. Keep it off of the battery for 30-60 seconds.

How many miles do you have to drive after disconnecting battery? ›

When a car's battery dies or is disconnected, the computer resets, erasing the internal emission monitors required to pass a smog test. You'll be good to go once you drive 100 to 200 miles with the new battery.

How much does it cost to reset an ECU? ›

You should expect to pay between $150 and $300 at a local repair shop or service center just to have the ECU inspected and tested. In many cases, the faulty ECU can be repaired or reprogrammed, and this type of repair will usually run between $300 to $750, depending on the make and model of your vehicle.

Does disconnecting car battery cause problems? ›

Disconnecting or replacing a battery on a computer-equipped vehicle may cause starting, driveability and a number of other problems, including loss of air conditioning, power accessory functions (door windows, seats, sunroof), false warning lights, even damage to certain electronic modules!

Does touching the battery cables together to reset computer? ›

See all 2 photos Connecting the positive and negative battery cables together for approximately 5 minutes will drain all of the capacitors in the computers and forces them to cold reboot. This is a very common fix for communication problems.

What happens if you disconnect the positive terminal first? ›

It's important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first.

How many miles is a complete drive cycle? ›

Drive cycles vary by manufacturer and can be reset in as little as 20 miles by a qualified technician (like us) since we have the knowledge and experience but if the normal everyday driver just drives 75-100 miles like they normally would (a mix of highway and city driving) the drive cycle can be completed.

Does ECU reset improve fuel economy? ›

For example, it's a common belief that remapping a vehicle has no effect on fuel economy, however, this technically isn't true. As the result of ECU remapping, a car usually sees an increase in power, which can come at the expense of higher fuel consumption.

How long does it take to reset a drive cycle? ›

15 minutes of steady driving on an expressway/highway followed by 20 minutes of stop-and-go driving with at least four 30-second idle periods. Allow the vehicle to sit for at least eight hours without starting the engine.

Does removing ECU fuse reset ECU? ›

Another way to reset your ECU system

Pull out your car's key. Pull out the fuse as well. Wait for 15 seconds and put it back in.

Is disconnecting negative terminal enough? ›

Q: Can you just disconnect the negative terminal? You can disconnect the battery's negative cable. All you are required to do is to locate the negative polarity of the battery and disconnect the terminal. Avoid the negative terminal to make contact with the positive one.

Can a scanner reset the ECU? ›

The Primary purpose of OBD Scanner is to provide data on Performance checks on the car - using data from engine and transmission and finding in faults. However - resetting ECU is not something which OBD Scanners are capable of.

What is hard and soft reset in ECU? ›

Soft resets are usually conducted in an attempt to fix malfunctioning applications or because they're required for software installation. Soft reset contrasts with hard reset, which removes all user data, settings and applications and returns a device to the same state it was in when it shipped from the factory.

What happens if you master reset your car? ›

A master reset will erase all settings on your SYNC System such as navigated routes and the phone book for the sync system. By removing the nav chip or SD card, you're able to save this valuable information.

What are symptoms of ECU failure? ›

Lucas Auto Care lists the symptoms of a bad ECU below.
  • Engine Lags or Surges. Because the ECU controls your engine's timing and fuel usage, you might notice engine performance issues such as lagging or surging in the module is going bad. ...
  • Engine Misfires and Stalls. ...
  • Your Car Won't Start. ...
  • Check Engine Light Alert.
15 Dec 2020

How do I reset my ECU without a scanner? ›

How to Reset the ECU/ECM Without Disconnecting the Battery:
  1. Pop the hood and locate the fuse box.
  2. Remove the fuse cover, then the ECU/ECM fuse.
  3. Leave the fuses for at least 10 seconds or up to 15 minutes.
  4. Reinstall the car computer fuse and replace the fuse cover.
  5. Take out your vehicle for a test drive.

What can damage an ECU on a car? ›

One of the main causes is a short circuit in the wiring or in components, which can cause them to burn out. This short circuit is often caused by external influences, such as the wrong start of the car.

Which battery terminal should you always disconnect first? ›

When disconnecting the cables from the old battery, disconnect the negative first, then the positive. Connect the new battery in the reverse order, positive then negative.” When you are replacing your car battery, It isn't always easy to remember the order in which to disconnect and reconnect the terminals.

How long does it take for battery to reset? ›

A jump-start usually takes about two minutes and up to five minutes with colder weather. After successfully starting the car, you need to drive for at least 15 minutes to recharge the battery.

What should you not disconnect when disconnecting a car battery? ›

You should never attempt to disconnect your car's battery while your car is powered on. We'd also recommend using safety equipment, like gloves and safety goggles, if you have them on hand.

Do I need to reprogram my car after battery replacement? ›

The new battery does not have to be configured for the most current car models. Banner conclusion: No registration required; a check of the electrical functions after changing the battery is recommended.

Can jumpstarting a car damage the ECU? ›

Blown Engine Control Unit (ECU)

A blown ECU can occur if there is a voltage spike when jumpstarting. This impacts the alternator and other electrical components such as the fuel pump, onboard computer and possibly the fuses.

How do I know if my ECU is working? ›

Here are the most common symptoms of a bad ECU:
  1. Check Engine Light stays on after resetting.
  2. Car was jump started on reverse polarity.
  3. Engine turning off for no reason.
  4. Water Damage or Fire Damage on the ECU.
  5. Apparent loss of spark.
  6. Apparent loss of injection pulse or fuel pump.
  7. Intermittent starting problems.
  8. Overheating ECU.

Can disconnecting battery damage alternator? ›

If your alternator is malfunctioning by over-charging your battery, disconnecting it may allow the alternator to provide an even higher voltage to the car electronics, and potentially damage those sensitive components.

How many minutes does the battery be removed if to reset the BIOS and clock information? ›

Wait 1–5 minutes, then reconnect the battery. Put the computer cover back on. Plug the computer and all devices back in.

What happens if you only disconnect the positive to a car battery? ›

If you disconnect the positive cable first, you might have several adverse effects including: Tools creating an arc of electricity. Shorting out electrical components. Blowing fuses.

Do I disconnect the positive or negative to check the alternator? ›

You'll disconnect the negative battery terminal to test the alternator. If you disconnect the positive battery terminal it could cause serious damage to your car's computer system.

Do you connect red or black first? ›

When you connect the cables, start with the positive/red one onto the positive battery cable and it will not spark. Now connect the negative cable (black one) to a piece of metal that is away from the battery, which means it is away from any hydrogen gas emitted by the battery.

What happens to car computer when battery is disconnected? ›

Disconnecting or replacing a battery on a computer-equipped vehicle may cause starting, driveability and a number of other problems, including loss of air conditioning, power accessory functions (door windows, seats, sunroof), false warning lights, even damage to certain electronic modules!

How do I refresh my car ECU? ›

How to Reset the ECU/ECM Without Disconnecting the Battery:
  1. Pop the hood and locate the fuse box.
  2. Remove the fuse cover, then the ECU/ECM fuse.
  3. Leave the fuses for at least 10 seconds or up to 15 minutes.
  4. Reinstall the car computer fuse and replace the fuse cover.
  5. Take out your vehicle for a test drive.

How long should I disconnect battery to clear codes? ›

Leaving the battery disconnected for about 15 minutes will ensure the vehicle systems will completely reset when you reconnect the battery. Secure the negative cable back to the terminal and cover it with the cap (if applicable). Disconnecting the battery will clear the error codes and reset the check engine light.

How long do you hold battery cables together to reset computer? ›

4) Connect the positive and negative battery cables together for approximately 5 minutes. This will drain all of the capacitors in the computers and forces them to cold reboot.

How much does an ECU reset cost? ›

You should expect to pay between $150 and $300 at a local repair shop or service center just to have the ECU inspected and tested. In many cases, the faulty ECU can be repaired or reprogrammed, and this type of repair will usually run between $300 to $750, depending on the make and model of your vehicle.

Is it a good idea to disconnect car battery? ›

If a vehicle and its battery are left unattended for a long period, probably a month, then it might result in the damage of the battery and could even introduce the need for a replacement. Therefore, it is recommended to disconnect the battery if in case you intend to go on a vacation or such.


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