The engine control system consists of three groups including sensors (and sensor output signals), engine ECU, and actuators. This chapter explains the sensors (signals), power circuitry and ground circuitry, and sensor terminal voltages. The engine ECU functions are divided into EFI control, ESA control, ISC control, diagnosis function, fail-safe and backup functions, and other functions. These functions and the actuator functions are explained in separate chapters.
Preliminary Knowledge
The power circuitry is the electrical circuits that supply power to the engine ECU. These electric circuits include the ignition switch, the EFI main relay, etc. The power circuitry actually used by the vehicle consists of the following two types.
1. Control by ignition switch
As shown in the illustration, the diagrams show the type in which the EFI main relay is operated directly from the ignition switch. When the ignition switch is turned on, current flows to the coil of the EFI main relay, causing the contacts to close. This supplies power to the +B and +B1 terminals of the engine ECU. Battery voltage is supplied at all times to the BATT terminal of the engine ECU to prevent the diagnostic codes and other data in its memory from being erased when the ignition switch is turned off.
2. Control by engine ECU
The power circuitry in the illustration is the type where operation of the EFI main relay is controlled by the engine ECU. This type requires that power be supplied to the engine ECU for several seconds after the ignition switch is turned OFF. Therefore, the turning ON and OFF of the EFI main relay is controlled by the engine ECU. When the ignition switch is turned ON, battery voltage is supplied to the IGSW terminal of the engine ECU, and the EFI main relay control circuitry in the engine ECU sends a signal to the M-REL terminal of the engine ECU, turning 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 the +B terminal of the engine ECU. Battery voltage is always supplied to the BATT terminal for the same reason as for the control by ignition switch type. In addition, some models include a special relay for the air-fuel ratio sensor heater circuitry which is required large amount of current.
REFERENCE:
In models where the engine ECU controls the engine immobiliser system, the EFI main relay is also controlled by the key unlock warning switch signal.
Ground Circuitry
The engine ECU contains the following three basic ground circuits.
1. Ground for engine ECU operation (E1)
The E1 terminal is the engine ECU unit ground terminal, and is normally connected close to the air intake chamber of the engine.
2. Sensor grounds (E2, E21)
The E2 and E21 terminals are sensor ground terminals, and these are connected to the E1 terminal in the engine ECU. These prevent the sensors from detecting erroneous voltage values by keeping the sensor ground potential and engine ECU ground potential at the same level.
3. Grounds for actuator operation (E01, E02)
The E01 and E02 terminals are actuator ground terminals, such as for the actuators, ISC valve, and air-fuel ratio sensor heater, and, as with the E1 terminal, they are connected close to the air intake chamber of the engine.