The engine control unit (ECU) in a Toyota Prius is the computer responsible for operating all of the engine's electronic components. This computer monitors data from various sensors throughout the vehicle in order to determine its operational state. When the ECU senses a problem with the engine or one of its related systems it stores a code in its flash memory and turns on the service engine soon (SES) light. A computerized scan tool is required to reset these codes and return the computer to its normal state.
Place the car's transmission in park and apply the parking brake. Turn the ignition to the "OFF" position to kill the engine. Rotate the ignition back to the "ON" position, but do not start the engine.
Connect the scan tool's data connector to the vehicle's 16-pin diagnostic data port, located underneath the driver's side dashboard/footwell area. Power on the scan tool.
Select "ECU" from the scan tool's main menu. Choose "Codes," then select "Clear all current and stored DTC's." DTC is an abbreviation for "diagnostic trouble codes."
Wait for the scan tool to clear the codes. The display will read "All codes cleared." Unplug the scan tool and start the vehicle. Ensure that the SES light is not turned on. The ECU is now reset.
