Isuzu KB P190. Manual - part 329

6E-282  Engine Control System (4JH1) 

Installation Procedure 

1. Set the vacuum pressure sensor on the bracket

and tighten a bolt. 

2. Connect a harness connector to the vacuum

pressure sensor. 

3.  Connect the negative battery cable. 

 

Vehicle Speed Sensor (VSS) Replacement 

Removal Procedure 

M/T & A/T (4WD) 

1.  Disconnect the negative battery cable. 

2.  Disconnect a harness connector from the vehicle

speed sensor (VSS). 

3.  Remove the VSS from the transmission. 

 
 

 
 
 

 

 
 

 
A/T (2WD) 

1.  Disconnect the negative battery cable. 

2.  Disconnect a harness connector from the vehicle

speed sensor (VSS). 

3. Loosen a bolt and remove the VSS from the

transmission. 

 

 

 

 
 

 

 
 

 
Installation Procedure 

M/T & A/T (4WD) 

1.  Install the VSS at the transmission. 

2.  Connect a harness connector to the VSS. 

3.  Connect the negative battery cable. 

 

M/T & A/T (4WD) 

1.  Set the VSS at the transmission and tighten a bolt.

2.  Connect a harness connector to the VSS. 

3.  Connect the negative battery cable. 

Engine Control System (4JH1)  6E-283 

Description And Operation 

Engine Control Module (ECM) Description

 

 

 

 

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The engine control module (ECM) is designed to

withstand normal current draws associated with vehicle

operation. Avoid overloading any circuit. When testing

for opens and shorts, do not ground or apply voltage to

any of the ECM circuits unless instructed to do so. In

some cases, these circuits should only be tested using 

a digital multi meter (DMM). The ECM should remain

connected to the ECM harness.  

The ECM is located on the floor panel. The ECM mainly

controls the following.  

•  The fuel system control  
• The exhaust gas recirculation (EGR) system

control 

•  The preheating (glow) system control  
•  The A/C compressor control 
•  On-board diagnostics for engine control 

The ECM constantly observes the information from

various sensor s. The ECM controls the systems that

affect vehicle performance. The ECM performs the

diagnostic function of the system. The ECM can

recognize operational problems, alert the driver through

the malfunction indicator lamp (MIL), and store

diagnostic trouble codes (DTCs). DTCs identify the

system faults to aid the technician in making repairs. 

 

 

 

 

 

 

ECM Voltage Description 

The ECM supplies a buffered voltage to various 

switches and sensor s. The ECM can do this because

resistance in the ECM is so high in value that a test

lamp may not illuminate when connected to the circuit.

An ordinary shop voltmeter may not give an accurate 

reading because the voltmeter input impedance is too

low. Use a 10-megaohm input impedance DMM, to 

ensure accurate voltage readings. The input and/or

output devices in the ECM include analog-to-digital 

converters, signal buffers, counters, and special drivers. 

The ECM controls most components with electronic

switches which complete a ground circuit when turned

ON. 

Aftermarket Electrical and Vacuum Equipment 

Aftermarket or add-on electrical and vacuum equipment 

is defined as any equipment which connects to the 

vehicle's electrical or vacuum systems that is installed

on a vehicle after the vehicle leaves the factory. No

allowances have been made in the vehicle design for

this type of equipment. No add-on vacuum equipment 

should be added to this vehicle. Add-on electrical 

equipment must only be connected to the vehicle's

electrical system at the battery power and ground. Add-

on electrical equipment, even when installed to these

guidelines, may still cause the powertrain system to 

malfunction. This may also include equipment not

connected to the vehicle electrical system such as

portable telephones and audios. Therefore, the first

step in diagnosing any powertrain fault is to eliminate all

aftermarket electrical equipment from the vehicle. After 

this is done, if the fault still exists, the fault may be

diagnosed in the normal manner. 

Electrostatic Discharge Damage 

Electronic components used in the ECM are often

designed to carry very low voltage. Electronic

components are susceptible to damage caused by

electrostatic discharge. By comparison, as much as

4,000 volts may be needed for a person to feel even the

zap of a static discharge. There are several ways for a

person to become statically charged. The most

common methods of charging are by friction and 

induction. 

•  An example of charging by friction is a person 

sliding across a vehicle seat. 

 

6E-284  Engine Control System (4JH1) 

Important:  

To prevent possible electrostatic discharge damage,

follow these guidelines: 

•  Do not touch the ECM connector pins or soldered

components on the ECM circuit board. 

•  Do not open the replacement part package until

the part is ready to be installed. 

•  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

following symbols when commanded ON: 
  

 

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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 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 
 

 
 
 

 

 

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The accelerator pedal position (APP) sensor is mounted 

on the throttle assembly. The engine control module

(ECM) uses the APP sensor s 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 intake throttle

assembly. The idle switch is part of the APP sensor

assembly. 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.  

 

 

 

 

 

 

 

Engine Control System (4JH1)  6E-285 

Crankshaft Position (CKP) Sensor  

 

 

 

 

 

 

 

 

 

 

 

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Legend 
  1.  Crankshaft Position (CKP) Sensor  

 2. Flywheel 

 3. Slit 

 

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.  

 

 

Engine Coolant Temperature (ECT) Sensor  

- Amplitudes of CKP sensor signal (CH1) increase 

as engine speed increases. 

- Each waveform cycle shorten as the engine 

speed increases. 

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

 

CH1  

0V 

CH2  

0V 

 

 

 

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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.