The common rail fuel injection system consists of
sensors which detect the condition of the diesel
engine, an engine electronic control unit (engine-
ECU) which controls the system based on signals
from these sensors, and actuators which operate
according to control commands from the engine-

ECU. The engine-ECU carries out activities such as
fuel injection control and idle speed control. In addi-
tion, the engine-ECU is equipped with several self-
diagnosis functions which make troubleshooting eas-
ier in the event that a problem develops.

FUEL INJECTION CONTROL
The injector drive time, the injection timing and the
fuel pressure are controlled so that the appropriate
quantities of fuel are supplied to the engine in
response to engine conditions which can change fre-
quently. A single injector is mounted at each cylinder.
The supply pump increases the fuel pressure to the
pressure which is required for high-pressure injec-
tion, and then send the fuel each injector.

IDLE SPEED CONTROL
The idle speed is kept at the optimum speed by con-
trolling the fuel injection quantity in accordance with
changes in idling conditions and engine load during
idling.

The engine-ECU drives the fuel injector to keep the
engine running at the pre-set idle target speed in
accordance with the engine coolant temperature and
A/C and other electrical load.

SELF-DIAGNOSIS FUNCTION

• When an abnormality is detected in any of the

sensors or actuators, the engine warning lamp
illuminates to warn the driver.

• When an abnormality is detected in any of the

sensors or actuators, a diagnosis code number
corresponding to the problem which occurred is
output.

• The RAM data relating to the sensors and actua-

tors which is stored in the engine-ECU can be
read using the M.U.T.-III. In addition, the actuator
can be force-driven under certain conditions.

OTHER CONTROL FUNCTIONS

1. Power Supply Control

When the ignition switch ON signal is input by the

ignition switch, the engine-ECU turns ON the
power transistor for controlling the engine control
relay. As a result, current flows through the coil in
the engine control relay, causing the relay switch
to turn ON and supply power to the sensors and
actuators.

2. Glow Control

Refer to GROUP 16
(Refer to , GROUP 16

− Glow System).

3. EGR Control

Refer to GROUP 17
[Refer to , GROUP 17

− Engine And Emission Con-

trol

− Exhaust Gas Recirculation (EGR) System].

4. A/C Relay Control

Turns the compressor clutch of the A/C ON and OFF.

5. Condenser Fan Motor Relay Control

Controls the condenser fan motor relay based on the

A/C switch, A/C load signal, engine coolant tem-
perature and vehicle speed input signals.

6. PTC Heater Relay Control <Vehicle with PTC

heater>

The PTC heater is turned ON is accordance with the

A/C operation at the engine cold state.

7. DPF System Control <Euro5>

[Refer to GROUP 17

− Emission Control − Diesel

Particulate Filter (DPF) System <Euro5>

− Gen-

eral Information (DPF system) ].

8. Variable Geometry Turbocharger Control

<Euro5>

Performing the duty control over the variable geome-

try control solenoid valve, the engine-ECU opens
and closes the nozzle vane located in the turbo-
charger assembly. This allows the boost pressure
to be obtained in accordance with the engine
operation.

9. Alternator Output Current Control <Euro5>

GENERAL INFORMATION

DIESEL FUEL

13A-7

Prevents the alternator output current from increas-

ing suddenly and the idle speed from varying
such as when the headlamp is turned on.

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