Lexus IS200 ECU-EFI Power Source Circuit and Wiring Diagram. When the ignition switch is turned ON, battery positive voltage is applied to terminal IGSW of the engine ECU and the EFI main relay (Marking: EFI) control circuit in the engine ECU sends a signal to the terminal MREL of the engine ECU switching on the EFI main relay.
This signal causes current to flow to the coil, closing the contacts of the EFI main relay and supplying power to terminals +B of the engine ECU. If the ignition switch is turned off, the engine ECU continues to switch on the EFI main relay for a maximum of 2 seconds for the initial setting of the ISC valve.
The following figure illustrates the Lexus IS200 ECU-EFI Power Source Circuit and Wiring Diagram.