The ECU on the Toyota FJ Cruiser is the computer or brain of the vehicle. It monitors engine performance and dictates how the engine adjusts to driving conditions. It regulates the amount of fuel being sent to the engine, the timing of the spark and just about everything else that helps the engine perform. Drivers occasionally might have to reset the FJ Cruiser's ECU for troubleshooting purposes.
Remove the negative battery cable from the battery terminal. Remove the positive battery cable from the positive battery terminal using a socket and ratchet.
Leave the battery disconnected for five minutes. The ECU retains memory as long as it has electrical power. Removing the battery removes the electrical power from the ECU and causes it to reset.
Reconnect the negative and positive battery cables to their respective terminals using the socket and ratchet.