There are a couple different levels that you may be talking about. The first low level relearn procedure is when the ECM is reset or the codes are cleared. It usually takes at least two ignition cycles and two days of driving for the ECM to come out of default. The other Relearn procedure can only be performed with a professional scan tool. Through the scan tool the user is able to reset fuel trims and a few other parameters. I hope this helps but if there is more to the question. Feel free to write back.
Answers & Comments
There are a couple different levels that you may be talking about. The first low level relearn procedure is when the ECM is reset or the codes are cleared. It usually takes at least two ignition cycles and two days of driving for the ECM to come out of default. The other Relearn procedure can only be performed with a professional scan tool. Through the scan tool the user is able to reset fuel trims and a few other parameters. I hope this helps but if there is more to the question. Feel free to write back.