The electronic control unit, or ECU, is the brains of your Honda Civic. The ECU is capable of doing thousands of calculations per second and monitors every aspect of the operation of your vehicle. It controls the air-to-fuel mixture, the fuel economy and limits the speed of the vehicle in order to conform to all state laws. You cannot operate the vehicle if you remove the ECU but you can replace its chip with an aftermarket, high-performance chip that will allow your Civic to run faster.
Prop open the hood and find the battery. Use a 10mm socket wrench to remove the two retaining bolts that secure the battery belt. Remove the belt.
Loosen the nuts that secure the battery cables. Start with the black negative cable and then detach the red positive cable. Remove the battery.
Locate the ECU, which is large, flat, plastic component that is immediately in front of the battery position.
Loosen the ECU's three retaining bolts.
Remove the front plastic cover to the ECU with your hands. Disconnect the three large wiring harnesses, which are attached with clips, from the back of the ECU.
Pull the ECU toward the front of vehicle and remove it. Install the new aftermarket ECU and reconnect the wiring harnesses. Replace the front plastic cover and install the three mounting bolts.
Replace the battery in the tray and reconnect the battery cables. Replace the battery belt and battery belt retaining bolts. Close the hood.
