We remap cars using only the best custom files, increase mpg and bhp. We have dealer level diagnostic equipment. Approved slt dealer. The engine control unit (ECU) is basically a computer that controls how the engine works, a bit like a brain.But the default settings – or maps – are not necessarily the best they could be, as manufacturers who sell their cars around the world have to take into account different climates, fuel qualities and laws when they program the software.