A failure of the engine control unit may imply very serious cost of repair. In many situations it is necessary to replace the whole component. You purchase a new part you may have to pay an astronomical amount of money which, in the case of older cars, may exceed that value of the vehicle itself. Needless to add that it is not very cost-effective. Therefore, it is a good idea to consider a cheaper solution especially that a used engine controller can serve you exactly like a new one.