Isuzu KB P190. Manual - part 824

Engine Management – V6 – Diagnostics 

Page 6C1-2–18 

 

4 

Diagnostics Starting Point 

4.1 Basic 

Requirements 

Basic Knowledge Required 

 

A lack of basic understanding regarding 
electronics, electrical wiring circuits and use 
of electrical circuit testing tools when 
performing an engine management system 
diagnostic procedure could result in incorrect 
diagnostic results or damage to engine 
management system components. 

Understanding of the following is required to perform the diagnostic procedures detailed in this Section. Refer to 8A 
Electrical - Body and Chassis and to Basic Tools Required. 

• 

Basic electronics, 

• 

Electrical wiring circuits, 

• 

Electrical circuits testing, and 

• 

Correct use of the basic engine management system diagnostic tools. 

In addition, understanding of the engine management system is essential to prevent misdiagnosis and component 
damage. Refer to 6C1-1 Engine Management – V6 – General Information. 

Basic Tools Required 

 

Use of incorrect electrical circuit diagnostic 
tools when performing the Engine 
Management diagnostic procedures could 
result in incorrect diagnostic results or 
damage to engine management system 
components. 

The following electrical circuit testing tools are required to perform the diagnostic procedures detailed in this Section.  

• 

Tech 2,  

• 

Test lamp, refer to 8A Electrical - Body and Chassis, and 

• 

Digital multimeter with 10 M

Ω impedance, refer to 8A Electrical - Body and Chassis. 

4.2 Diagnostic 

Precautions 

The following precautions must be observed when performing the powertrain diagnostic procedure, otherwise incorrect 
diagnostic results or damage to engine management system components will occur: 

• 

Disconnection of the battery affects certain vehicle electronic systems. Refer to 6D1-3 Battery – V6 before 
disconnecting the battery. 

• 

Disconnect the battery negative lead when performing the following procedures: 

− 

Disconnecting the ECM connectors, or 

− 

Charging the battery. 

• 

Disconnect the battery terminal lead and the ECM connectors before attempting any electric arc welding on the 
vehicle. 

Engine Management – V6 – Diagnostics 

Page 6C1-2–19 

 

• 

Do not start the engine if the battery terminal is not properly secured to the battery. 

• 

Do not disconnect or reconnect the following while the ignition is switched on or when the engine is running: 

− 

Any engine management system component electrical wiring connector, or 

− 

Battery terminal leads. 

• 

Ensure the correct procedure for disconnecting and connecting engine management system electrical wiring 
connectors is always followed. For information on the correct procedure for disconnecting and connecting specific 
wiring connectors, refer to 6C1-3 Engine Management – V6 – Service Operations. 

• 

Ensure that all wiring harness connectors are fitted correctly. 

• 

When steam or pressure cleaning engines, do not direct the cleaning nozzle at engine management system 
components. 

• 

Do not clear any DTCs unless instructed. 

• 

The fault must be present when using the diagnostic trouble code (DTC) diagnostic tables. Otherwise, 
misdiagnosis or replacement of good parts may occur. 

• 

Do not touch the ECM connector pins or soldered components on the ECM circuit board to prevent ECM 
Electrostatic Discharge damage. Refer to 8A Electrical - Body and Chassis for information on Electrostatic 
Discharge. 

• 

Use only the test equipment specified in the diagnostic tables as other test equipment may give incorrect results or 
damage good components. 

• 

The ECM is designed to withstand normal current draw associated with vehicle operations. However, the following 
fault conditions or incorrect test procedure may overload the ECM internal circuit and damage the ECM: 

− 

A short to voltage fault condition in any of the ECM low reference circuits may cause internal ECM and / or 
sensor damage. Therefore, any short to voltage fault condition in the ECM low reference circuits must be 
rectified before replacing a faulty component. 

− 

A short to ground fault condition in any of the ECM 5 V reference circuits may cause internal ECM and / or 
sensor damage. Therefore, any short to ground fault condition in the ECM 5 V reference circuits must be 
rectified before replacing a faulty component. 

− 

When using a test lamp to test an electrical circuit, do not use any of the ECM low reference circuits or 5 V 
reference circuits as a reference point. Otherwise, excessive current draw from the test lamp may damage 
the ECM. 

• 

Disregard DTCs that set while performing the following diagnostic Steps: 

− 

Using Tech 2 actuator tests, or 

− 

Disconnecting an engine management system sensor connector then switching on the ignition. 

• 

After completing the required diagnostics and service operations, road test the vehicle to ensure correct engine 
management system operation. 

4.3 Preliminary 

Checks 

The preliminary checks are a set of visual and physical checks or inspections that may quickly identify engine 
management system fault condition. 

• 

Refer to the appropriate Service Techlines for relevant information regarding the fault condition. 

• 

Ensure the battery is fully charged. 

• 

Inspect the battery connections for corrosion or a loose terminal. 

• 

Ensure that all engine management system related fuses are serviceable. 

• 

Inspect for incorrect aftermarket theft deterrent devices, lights or mobile phone installation. 

• 

Ensure there is no speaker magnet positioned too close to any electronic module that contains relays. 

• 

Inspect the engine wiring harness for proper connections, pinches or cuts. 

• 

Ensure that all engine management related electrical wiring connectors are fitted correctly. 

• 

Inspect the ECM ground connections for corrosion, loose terminal or incorrect position. 

Engine Management – V6 – Diagnostics 

Page 6C1-2–20 

 

• 

Ensure the resistance between the ECM housing and the battery negative cable is less than 0.5 

Ω. 

• 

Check the ECM bracket fasteners for correct torque value. 

• 

Check all engine management related components for correct installation. 

• 

Inspect the vacuum hoses for splits, kinks, oil contamination and proper connections, refer to the vehicle emission 
control information label. Check the hoses thoroughly for any type of leak or restriction. 

• 

Inspect the air intake ducts for being collapsed, split or for having damaged areas. 

• 

Inspect for air leaks at the throttle body mounting area, mass air flow (MAF) sensor, intake manifold and intake 
manifold sealing surfaces. 

• 

Check for wiring harness routing that may be positioned too close to a high voltage or high current device such as 
the following: 

− 

Secondary ignition components, and 

− 

Motors and generators. 

N O T E  

High voltage or high current devices may induce 
electrical noise on a circuit, which can interfere 
with normal circuit operation. 

4.4 

Diagnostic System Check 

Description 

The engine management diagnostic procedure is organised in a logical structure that begins with the Diagnostic System 
Check. The Diagnostic System Check directs the diagnostic procedure to the logical steps necessary to diagnose an 
engine driveability fault condition. 

Test Description 

The following numbers refer to the step numbers in the diagnostic table: 

6 

Tests the integrity of the GM LAN serial data communication circuit. A PIM DTC sets if the PIM detects a fault 
condition in the communication circuit. A fault condition on the serial data communication circuit may trigger 
multiple DTCs on other sensors and components. 

Step Action 

Yes 

No 

1 

Have you read the basic requirements? 

Go to Step 2 

Refer to 

4.1 Basic 

Requirements 

2 

Have you read the diagnostic precautions? 

Go to Step 3 

Refer to 

4.2 Diagnostic 

Precautions 

3 

Have you performed the preliminary checks? 

Go to Step 4 

Refer to 

4.3 Preliminary 

Checks 

4 

Using Tech 2, attempt to communicate with the PIM. 

Does the PIM fail to communicate? 

Refer to 6E1 

Powertrain Interface 

Module – V6 

Go to Step 5 

5 

Does DTC B3902, C0550, U2100, U2105, U2106, P0633, or P1611 
also set in the PIM? 

Refer to 6E1 

Powertrain Interface 

Module – V6 

Go to Step 6 

6 

Using Tech 2, view and record DTCs set at the ECM and TCM. 

Does Tech 2 display any DTC? 

Go to Step 7 

Refer to 

5.1 Symptoms 

Diagnosis Table 

Engine Management – V6 – Diagnostics 

Page 6C1-2–21 

 

Step Action 

Yes 

No 

7 

Does Tech 2 display multiple DTCs? 

Go to Step 8 

Go to the diagnostic 

table of the DTC 

displayed. Refer to 

7.1 DTC List 

8 

Does Tech 2 display any serial data communication circuit DTC? 

Go to the 

appropriate serial 

data communication 

circuit DTC table. 

Refer to 

7.1  DTC List 

Go to Step 9 

9 

Does Tech 2 display any immobiliser circuit DTC? 

Go to the 

appropriate 

immobiliser circuit 

DTC table. Refer to 

7.1  DTC List 

Go to Step 10 

10  Refer to the DTC Table of the fault condition that is most likely to 

trigger multiple DTCs. Refer to 1.2  Diagnostic Trouble Code Tables 
in this Section. 

— 

— 

When all diagnosis and repairs are completed, check the system for correct operation.