How Long to Disconnect Battery to Reset Ecu? (Explained)

An ECU or Electronic Control Unit is a device to perform specific tasks and receive signals from different parts of your car. So, you might need to reset the ECU for different reasons. If you want to reset the ECU, you have to disconnect the battery also.

But you might know that after disconnecting the battery, some current is still passing through. So, you might be confused about how long to disconnect the battery to reset the ECU. If you don’t allow the battery some time, the resetting might not be effective. So, you should know the time of disconnecting the battery.

Can you reset ECU by disconnecting battery? Does disconnecting the battery reset codes?

No, you can’t reset ECU by disconnecting the battery always. Because instant disconnecting the battery might not reset the ECU. Sometimes, we disconnect the car battery for a short time. Bu ECU requires more time to be reset.

If you disconnect the battery for a short time, the ECU might also pass some current through it. So, resetting will not be effective. But if you disconnect the battery for a sufficient time, the ECU will be reset and the car will start.

Whether disconnecting the battery resets codes or not depends on how much time you disconnect the battery. The codes need enough time to reset.

So, if you disconnect the car’s battery for enough time, the codes will get time to be reset. So, whether the codes will reset or not depends on the time of disconnecting.

How long to disconnect battery to reset ecu?

It will take about 15 minutes to disconnect the battery to reset the ECU or electronic computer unit. When you want to reset the ECU, you have to wait sometime so that the battery is fully disconnected. Otherwise, some current will still be in the ECU and the ECU codes will not be reset.

However, disconnecting the battery is a pretty common way to reset the ECU. But you can also reset the ECU by other methods. Among them, disconnecting the battery is the easiest. But many people think that only disconnecting the battery for a while will reset the ECU. Let’s see whether disconnecting the battery will be enough to reset the ECU or not. Moreover, the time should also be enough for disconnecting.

BMW:

If you have the BMW ECU, you still have to allow some time so that the ECU can reset. Because the electronic computer in your car needs time to reset. If you disconnect the connection to the battery.

But with this, the ECU will not be reset. Generally, BMW and other cars’ ECUs pass-through current for 10 to 15 minutes after disconnecting the battery. So, you can’t reset the ECU just after disconnecting the battery.

When you reset the ECU, it will not harm the battery either. But if you can change certain features. On the other hand, when you will disconnect the battery, some functions of the ECU will also be changed.

Sometimes, people disconnect the battery for a long time. This can remove all the coded data from the ECU. So, you should know how long you can disconnect your car battery.

So, 15 minutes will be enough for BMW ECU. At this time, the car’s battery will be disconnected fully and the reset will also be effective. If you want to reset the ECU from the beginning, you have to allow 15 minutes.

Because in 5 to 15 minutes, all the previous data will be removed and the ECU will be reset.

2 reasons why disconnecting car battery to reset ECU takes long

You might have thought that disconnecting the car battery will reset the ECU. But it takes time. Let’s see what are the reasons why disconnecting the car battery to reset ECU takes a long time.

Disconnecting needs to be completed:

If you disconnect the car’s battery for a short time, disconnecting is not completed immediately. All the connections and current passing should be stopped when you disconnect the car battery to reset the ECU.

Especially when you want to disconnect the battery to reset the ECU, you need to wait for some time. Because current can be still present in the ECU. It can still have data and codes from the previous setting. That’s why you should wait at least 15 minutes after disconnecting the car battery.

All memories of ECU should be deleted:

When you want to reset the ECU of your car, the previous memories of the ECU should be forgotten or removed. So, when you disconnect the car battery, memories of the ECU start to disappear. It can take up to 5 to 15 minutes.

So, if you don’t wait at least 15 minutes, some data might still be present on the ECU. The ECU will not be reset then. So, you have to reset it again.

That’s why if you want to reset the ECU effectively, you have to give it at least 15 minutes.

Will disconnecting car battery harm computer? What does it do?

No, disconnecting your car battery will not harm the computer. Though permanent damage will not occur, some effects might be present in the computer after disconnecting the car battery.

For example, if you disconnect the car battery for a couple of minutes, it might preset the radio stations. Moreover, the ECU, or electronic computer unit, can forget the previously learned shift points. Because the ideal air to fuel ratio mixture might be forgotten by the ECU.

These can lead to harm to the internal parts of your car. Sometimes, disconnecting the car battery for a long time can remove all the previous data from the electronic computer system.

Generally, when you normally drive your car, the ECU tracks all the acceleration operations, air-to-fuel mixture ratio, and how the car operates for different purposes. But when you disconnect the car battery, the ECU will no longer get power to store this data.

So, all the memories of the ECU will be removed within 10 to 15 minutes. So, if you don’t code the data in the ECU again, it will not function properly. As a result, many of the car’s functions may be altered.

So, disconnecting the car battery will not harm the computer but it will reset the computer.

Do I disconnect the positive or negative to reset ECU?

You have to disconnect the negative terminal first to reset ECU or Electronic Computer Unit. Then you can disconnect the negative terminal.

Generally, the positive terminal of the car is connected to the parts that need electric power. So, if you want to disconnect the positive terminal first, you might get close to the electric power and get a shock.

This can lead to a dangerous situation. On the other hand, the negative terminal of the car is connected to some bolts inside the engine bay. So, disconnecting the negative terminal first will not cause harm or a dangerous situation. That’s why you should disconnect the negative to reset ECU.

How to disconnect a car battery to reset ECU?

Now that you know you can disconnect a car battery to reset ECU, you might want to know the process. Let’s see how you can disconnect a car battery safely to reset the ECU.

Get ready the necessary things:

First, you have to get all the necessary tools and accessories ready. For example, you will need safety goggles, hand gloves, a socket wrench, etc., to disconnect the car battery.

Make ready the car:

Then you have to make the car ready so that you can safely disconnect the battery. You have to park the car in a safe place and turn off the ignition. Then you have to take all the safety measures, like wearing goggles and gloves.

Detach the terminal:

Then you have to remove the negative and positive terminal. Now you have to remember that you should always remove the negative terminal first. Because the positive terminal is connected to all the electric power connections of the car.

So, removing the positive one might make it dangerous or you can experience an electric shock. So, you have to remove the negative terminal first, then you can remove the positive one.

Final Thoughts

It takes 10 to 15 minutes to reset the ECU or Electronic Computer Unit. That’s why it will take at least 15 minutes to disconnect the car battery to reset the ECU. If you don’t keep at least 15 minutes, the previous memories of the computer will be present, and the current will pass through it.