Isuzu N-Series. Manual - part 800

Engine Control System (4JH1) 6E-251

• Before removing the part from the package,

ground the package to a known good ground on
the vehicle.

• If the part has been handled while sliding across

the seat, while sitting down from a standing
position, or while walking a distance, touch a
known good ground before installing the part.

• Charge by induction occurs when a person with

well insulated shoes stands near a highly charged
object and momentarily touches ground. Charges
of the same polarity are drained off leaving the
person highly charged with opposite polarity.

Malfunction Indicator Lamp (MIL) Operation
The malfunction indicator lamp (MIL) is located in the
instrument panel cluster (IPC). The MIL will display the
CHECK ENGINE when commanded ON:

Legend

1. Malfunction Indicator Lamp (MIL)

The MIL indicates that an emission or performance
related fault has occurred and vehicle service is
required. The following is a list of the modes of
operation for the MIL:

• The MIL illuminates for approximately 2 seconds

when the ignition switch is turned ON, with the
engine OFF. This is a bulb test to ensure the MIL
is able to illuminate.

• The MIL remains illuminated after the engine is

started if the engine control module (ECM) detects
a fault. A DTC is stored any time the ECM
illuminates the MIL due to an emission or
performance related fault.

Engine Control Component Description

Accelerator Pedal Position (APP) Sensor & Idle
Switch

Legend

1. Accelerator Pedal Position (APP) Sensor
2. Accelerator Pedal Bracket
3. Idle Switch

The accelerator pedal position (APP) sensor is
mounted on the accelerator pedal bracket. The engine
control module (ECM) uses the APP sensors to
determine the amount of acceleration or deceleration
desired by the person driving the vehicle via the fuel
injection control.
The idle switch is also mounted on the accelerator
pedal bracket. The idle switch is a normally closed
type switch. When the accelerator pedal is released,
the idle switch signal to the ECM is low voltage.

Crankshaft Position (CKP) Sensor

N6A3899E

N6A3900E

N6A3885E

6E-252 Engine Control System (4JH1)

The crankshaft position (CKP) sensor is located on top
of the flywheel housing. There are 4 slits spaced 90

on the flywheel circumference. The CKP sensor is a
magnetic coil type sensor, which generates an AC
signal voltage based on the crankshaft rotational
speed. The ECM monitors both the CKP sensor and
injection pump camshaft position (CMP) sensor signals
to ensure they correlate with each other.
The following waveform aids to diagnose when there is
an oscilloscope or equivalent.

• Amplitudes of CKP sensor signal (CH1) increase

as engine speed increases.

• Each waveform cycle shorten as the engine speed

increases.

Engine Coolant Temperature (ECT) Sensor

Legend

1. Engine Coolant Temperature (ECT) Sensor

The engine coolant temperature (ECT) sensor is
installed to the thermostat housing. The ECT sensor is
a variable resistor. The ECT sensor measures the
temperature of the engine coolant. The engine control
module (ECM) supplies 5 volts to the ECT signal circuit
and a ground for the ECT low reference circuit. When
the ECT sensor is cold, the sensor resistance is high.
When the engine coolant temperature increases, the
sensor resistance decreases. With high sensor
resistance, the ECM detects a high voltage on the ECT
signal circuit. With lower sensor resistance, the ECM
detects a lower voltage on the ECT signal circuit.

Exhaust Gas Recirculation (EGR) Solenoid Valve

The engine control module (ECM) controls the exhaust
gas recirculation (EGR) flow amount based on the
engine speed, engine coolant temperature, intake air
temperature, barometric pressure and fuel injection
quantity. The ECM controls the EGR valve by
controlling the EGR solenoid valve. The mass air flow
(MAF) sensor monitors EGR gas flow amount. An
expected MAF amount should be detected while the
engine running.

Terminal: 90 (CH1), 91 (CH2) (+) / GND (-)
Scale: 10V/div 2ms/div
Condition: Approximately 1000RPM

CH1

CH2

N6A3820E

N6A3887E

N6A3888E

Engine Control System (4JH1) 6E-253

Intake Air Temperature (IAT) Sensor

The intake air temperature (IAT) sensor is fitted
between the air cleaner and turbocharger internal to
the mass air flow (MAF) sensor. The IAT sensor is a
variable resistor. The IAT sensor measures the
temperature of the air entering the engine. The engine
control module (ECM) supplies 5 volts to the IAT signal
circuit and a ground for the IAT low reference circuit.
When the IAT sensor is cold, the sensor resistance is
high. When the air temperature increases, the sensor
resistance decreases. With high sensor resistance, the
ECM detects a high voltage on the IAT signal circuit.
With lower sensor resistance, the ECM detects a lower
voltage on the IAT signal circuit.

Mass Air Flow (MAF) Sensor

The mass air flow (MAF) sensor is an air flow meter
that measures the amount of air that enters the engine.
It is fitted between the air cleaner and turbocharger. A
small quantity of air that enters the engine indicates
deceleration or idle. A large quantity of air that enters
the engine indicates acceleration or a high load
condition. The MAF sensor assembly consists of a
MAF sensor element and an intake air temperature
sensor that are both exposed to the air flow to be
measured. The MAF sensor element measures the
partial air mass through a measurement duct on the
sensor housing.

Vehicle Speed Sensor (VSS)

The vehicle speed sensor (VSS) is used by the engine
control module (ECM) and speedometer, which
generates a speed signal from the transmission output
shaft. The VSS uses a hall effect element. It interacts
with the magnetic field created by the rotating magnet
and outputs square wave pulse signal. The ECM
calculates the vehicle speed by the VSS.

N6A3889E

N6A3906E

Terminal: 68 (+) / GND (-)
Scale: 5V/div 50ms/div
Condition: Approximately 20km/h (12MPH)

N6A3821E

6E-254 Engine Control System (4JH1)

Fuel Injection System Description

Legend

1. Drive Shaft
2. Fuel Feed Pump
3. Pump Camshaft Position (CMP) Sensor
4. Fuel Injection Pump Control Unit (PCU)
5. Distributor Head
6. Constant Pressure Valve (CPV) Holder

7. Fuel Injection Solenoid Valve
8. Constant Pressure Valve (CPV)
9. Timing Control Valve (TCV)

10. Timer

11. Radial Plunger

Bosch VP44 Fuel Injection Pump
Instead of the previous face cam type, the radial
plunger distributor type injection pump utilizes a cam
ring to enable fuel injection at high-pressures, marking
it suitable for small, high-speed direct injection diesel
engines. This pump was developed to provide the
most suitable fuel injection quantity and injection timing
to satisfy the demand for engine reliability, driveability,
low smoke, low noise, high output and low exhaust
emissions.

The engine control module (ECM) calculates the
desired fuel injection quantity and timing using data
sent from various sensors. These desired data are
sent to the fuel injection pump control unit (PCU) via a
controller area network (CAN) communication bus.
The PCU also receives signals from the internal inputs:
pump camshaft position (CMP) sensor that is located
inside the fuel injection pump to determine the cam ring
rotation angle and the fuel injection pump speed. The
fuel temperature (FT) sensor is internal the PCU.
These values are used to compare the desired values
sent from the ECM then PCU determines the injection
timer piston position and fuel injection quantity, and
actuates timing control valve (TCV) & fuel injection
solenoid valve based on control maps in the PCU.

N6A3839E

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