The electronic control unit (ECU) is responsible for managing numerous aspects of a car's performance. When the unit is in need of service or replacement, it must be located, disconnected and removed from the vehicle. If you want to install an aftermarket performance chip, you will have to remove the ECU. On a Ford Focus, the ECU is located behind the glove box, so it can be serviced with relative ease and some basic hand tools.
Pop the hood of your Ford Focus to access the engine compartment. Use a wrench to loosen the nut on the negative battery terminal then pull the cable completely off of the terminal.
Open the glove box and remove all of its contents. Apply firm pressure to the plastic sides of the box, pressing toward the center until the plastic guide arm is free of its groove. Continue pulling the door open. The pressure will allow it to swing beyond its usual tilting point. Several electronic devices will now be exposed. The ECU is a metal box with a white sticker displaying a four-digit code.
Unplug the wiring harness from the hookup on the back of the ECU. Use a 10 mm socket to disconnect the bracket holding the ECU in place and pull the unit out of the glove box area. It can now be serviced or replaced as necessary. Simply reverse the above steps to reinstall the ECU.
