Car System

How Long Does It Take For Car ECU To Relearn Things?

Mike Cross
Updated Feb 16, 2022

So, you reset your cars ECU. You may have done this intentionally, or you may have done this on an accident. Well, now it has to relearn all the different things it knows. This relearning process takes time just like it takes us, humans, time to learn.

How long does it take the ECU to relearn though? Well, the answer to that question is what we are going to talk about today. Read on to learn how long it takes the ECU to relearn certain things, and also what the ECU is.

How Long Does It Take For Car ECU To Relearn Things?

What is ECU

Before we go into detail on how long it takes the ECU to relearn information, we are first going to cover what the ECU is. You may not that it is a part of your vehicle, but you might not know what it is or what it does. This is especially true if you accidentally reset your cars ECU by disconnecting the battery to work on something. Also, if your battery died, then the ECU might have got reset.

The ECU is one of the main brains of the car. ECU stands for Engine Control Unit. Another name for it is the Engine Control Module. The job of the ECU is to control different actuators in the engine to make sure that the engine runs at peak performance. It does this by knowing certain information. That information is how much air is going into the engine, how much exhaust is coming out, how much fuel is being injected into the engine, and other things like that. This is the information that an ECU has to relearn when it has been reset.

How Long Does it take for Car ECU to Relearn Things

So, now we can get back to the main question at hand, and that is how long does it take the ECU to relearn this information. Well, sadly there is no straight forward answer to this question. The amount of time can vary. A lot depends on how often you drive the vehicle, how long you drive it, and the style of driving you to do. Certain conditions have to be meet for the ECU to relearn certain things. Different things take different kinds of driving to be relearned.

Basic information

Basic information the ECU can normally relearn quickly. If you drive your car constantly for 20-25 minutes, then it might relearn the basic things of air intake and fuel injection. Other things though may take longer.

A lot also has to do with how you are driving. If you are driving slow, then the ECU is normally not able to relearn things as well. Sometimes it can take up to a week for the Engine Control Unit to relearn certain things, especially if you are not driving a lot. Don’t be surprised if it takes upwards of 100 miles of town driving to get the ECU to relearn everything.

Relearn Fast

What if you need the ECU to relearn fast because you have an inspection or something. This is common if you have an emission test. The car has to drive in a certain way to get the ECU in the ready mode for an emission inspection. If it is not ready, then it is an automatic failure. That means if your vehicles ECU has been reset recently, then it might not pass the emission test due to not being ready.

Well, luckily for you for the car to get to the ready status certain conditions have to be met. These conditions vary from make and model to make and model, but the following list of conditions is similar to what most cars have to do to get to the ready status or in other words have the ECU relearn things.

Using OBDII Drive Cycle to get ECU relearn

To get the ECU to relearn you have to do an OBDII Drive Cycle

A Typical OBD-II Drive Cycle consists of...

  1. Cold start (Coolant below 122 Degrees F).
  2. Five to eight-minute warm-up and idle.
  3. First acceleration to 55mph at half throttle with the air conditioning turned off.
  4. First steady cruise at 55mph for three minutes.
  5. First deceleration to 20mph.
  6. Second acceleration at 3/4 throttle.
  7. Second steady cruise at 60mph for five minutes.
  8. Second deceleration without applying the clutch or brake pedal.

If you do these things, then it will count as a drive cycle and help the ECU relearn things. This relearning will help get your car ready for an emission check. Like we have said, your vehicle may be a little different though, so look up specifics for your vehicle to help get your ECU ready for an emission check.

Read more: What Are The Best Bluetooth OBD2 Scanner In 2022?

The man do an emission check
The man do an emission check

Relearn Importantly

So, one other thing you may be wondering is if you should reset ECU or is it important for your ECU to relearn things? Well, the answer to should you reset your ECU is it depends on you. Some people find their car to drive better after resetting and letting the ECU relearn things, while others notice no difference. Honestly, your car should be relearning constantly. That ties into the second part.

Should you be worried about forcing your car’s ECU to relearn after a reset. The answer is no, not really. The car is constantly relearning all the time. If you just drive the specific conditions for the ECU to relearn will happen. You shouldn’t stress about making sure that it happens. The only time you should be worried if the right conditions are being met is if you have an emissions test soon. Other than that, the ECU will relearn at its own pace, kind of like how us humans learn at our own pace.


So, the answer to how long does it take an ECU to relearn is a complicated one. The real answer is it depends on how you drive. It could take as little as 30 minutes if you drive exactly in a specified way. Other times it may take a week or so. In the end, it does matter though because the engine control module is constantly learning and making sure your car is running optimally.

Mike Cross
Life is too short to drive with stock audio

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3 comments on “How Long Does It Take For Car ECU To Relearn Things?”

  1. Ive done everything i can think of to get my car 2006 buick lacrosse to pass emission test for inspection but keeps failing ive disconnected the battery had new muffler put on tail pipe new new vaccum for leak new gas cap new fuse Emissions etc still wont pass no defects are showing up but computor wont relearn for some unknown reason also drove it 500 miles since trying to get it inspected help please what else can i do its a nice car

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