The ECU is the electronic control unit on your Lexus SC400. Essentially, it is the "brain" of your automobile. It controls everything from ignition timing to fuel delivery. When the ECU fails to work properly, your vehicle will likely fail to start. When this happens, you must remove the ECU and take it to a repair shop to have it reprogrammed or you must replace it with a new one.
Disconnect the negative battery cable from the battery with a socket and ratchet.
Remove the fasteners that secure the passenger kick panel with a screwdriver. The kick panel is located on the right side of the lower dash between the dash and the floor.
Pull the kick panel away from the vehicle to expose the silver ECU.
Unplug the wiring harness from the ECU. There is a lock on each end of the harness. Pull up on the tab on each end to unlock the harness.
Remove the bolts that secure the ECU to the vehicle with a socket and ratchet.
Secure the new ECU onto the vehicle with the bolts, socket and ratchet.
Plug the wiring harness into the new ECU and push down on the locking tabs on both sides of the harness to lock it into place.
Secure the kick panel into place with the fasteners and screwdriver.
Reconnect the negative battery cable with the socket and ratchet.
