ECU Power Feeds

The ECU receives its ignition-switched power from the EFI main relay on all of Toyota's EFI systems. In addition to the ignition +B power feed, all P7 and TCCS ECUs have a direct battery feed, identified as BATT, supplied from either the EFI, STOP, or ECU +B fuse. The EFI main relay +B output is the power source which feeds the ECU and related engine control circuits. The direct battery feed (terminal BATT) serves to maintain voltage to the ECU keep alive memory when the ignition switch is off. Conventional EFI has no keep alive memory capabilities and, therefore, uses only an ignition switched power feed from the EFI main relay.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

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