Control Unit

The Electronic Control Unit (ECU) microprocessor receives input signals from various sensors, switches and ignition and starting system components. The ECU uses this information for controlling various functions. See OUTPUT SIGNALS .

The ECU has constant battery voltage at BATT terminal. The EFI main relay provides battery voltage to terminals +B and +B1 of ECU. The EFI main relay is activated when ignition is turned on.

The ECU contains a fail-safe function, used in case of sensor or switch failure. The fail-safe function uses preprogrammed values to provide a limp-in mode for minimal driveability or may shut off engine.

The ECU is equipped with a self-diagnostic function. Trouble codes are set by the malfunction of various engine sensors, switches or circuits and stored in the ECU memory. When trouble code is stored, the CHECK ENGINE light on the instrument panel will come on.

ECU LOCATION

Model	Location
Camry	Behind Glove Box
Celica, Corolla, Paseo & Tercel	Bottom Center Of Dash, In Front Of Console
Cressida, Land Cruiser & Supra	Above Glove Box
MR2	Left Rear Of Engine Compartment
Pickup & 4Runner	Behind Passenger-Side Kick Panel
Previa	Under Driver's Seat

NOTE: Components are grouped into 2 categories. The first category is INPUT DEVICES, which covers components that control or produce voltage signals monitored by the control unit. The second category is OUTPUT SIGNALS, which are components controlled by the control unit.