Es250 Power Circuits

Ensure ignition is off. Disconnect connectors from ECU. Remove locks so ECU connector can be easily backprobed. See Fig 1. Reconnect ECU connectors.
Turn ignition on. Using a DVOM, measure voltage between ground and ECU terminals BATT, B1 and E1. See Fig 2. Battery voltage should be present.
If battery voltage is not present, check 40-amp MAIN fuse and 15-amp EFI fuse. Also ensure wire harness is not open or shorted. If fuses and wire harness are okay and conditions indicate ECU may be faulty, substitute a known good ECU. If condition improves, replace original ECU.

Fig 1: Locating ECU Connector Locks (ES250 & LS400)

Fig 2: Identifying ECU Terminals (ES250)