The ECU, or engine control unit (also known as the engine control module), is a small computer that controls the major functions in your vehicle. The Toyota Avalon has many functions controlled by the ECU; a faulty ECU can make your vehicle inoperable. Replacing the Avalon's ECU may vary slightly from year to year, but the basics will be the same no matter what year-model it is.
Remove the battery cover to access the battery terminals. Disconnect the negative (-) battery cable with the pliers.
Open the glove box door and squeeze the outer part to remove the door. Locate the two screws behind the door to remove the glove box.
Access the ECU behind the glove box. Remove the electrical connectors by hand; remove the bolts mounting the ECU to the inner dash.
Install the new ECU in the same position. Replace the bolts and reconnect the electrical connectors.
Replace the glove box and the glove box door. Reconnect your battery.
