The main reason people reset ECU in their cars is that all automakers set default values for everything that is set in the ECU because some countries require lower settings due to different laws and climate, weather, and various other factors. This means that no ECU is set to maximum performance per country, which means that ECUs are only optimized for mixed environments.
This will prevent a car from performing at its best. The best way to change that and make your car the best is by remapping the ECU. You can also check the benefits of remapping using various online sources.
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The most common way to make changes to an ECU is to direct the ECU when a dedicated tuner is working on your vehicle's ECU with an OBD flash tool for better performance, or when the ECU can be replaced with a completely new control unit.
OBD, or on-board diagnostics, is a term that means self-diagnosis of a car (or motor vehicle) and the ability to report vehicle engines. Thanks to the integrated diagnostics, you can access the status information of your vehicle and various other subsystems to check and edit it if necessary.
With the tuning chip, however, it's just about processing vehicle control and handling. This is done with EPROM processing which, when done right, provides much better performance in many ways, including more power, lower emissions, cheaper fuel, and many other engine improvements.