When a car is removed from the production line, its engine control unit software is set by default, which works worldwide and takes into account factors such as different climates, road conditions, geographic conditions, different fuel quality, etc.
While these default settings may be the best overall setting for your overall vehicle, they may not be the most effective settings for your specific needs.
For example, if you want more power, by directing the ECU you can change the gear ratio, air/fuel ratio, and fuel flow in your car's powertrain to increase power, which usually affects fuel efficiency. You can also get the best services for diesel ECU remapping via http://refineddieselremapping.com.au/ in Australia.
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If you have exchanged some other parts to support high-performance parts for your car, eg. exhaust, you may also want to customize your control unit with a new modification. Each performance add-on requires assigning a different control unit to get the most out of it.
On the other hand, if your vehicle is a functioning vehicle, eg. if you have a company van, truck, or a company fleet car that has to travel a long way, you may want to adjust the ECU to increase fuel efficiency at lower production costs.
Get involved with a reputable and established tuning company with experience. They may be more expensive for some reason but they employ highly trained technicians, and their hardware and software are licensed and up to date.
You also need to pay attention to whether they offer insurance and whether they offer a guarantee. Both must be 'yes'.
An initial investment of a few hundred dollars plus can save you thousands of dollars in the long run. So don't risk your trip.