Isuzu KB P190. Manual - part 322

6E-254  Engine Control System (4JH1) 

Step Action 

Value(s) 

Yes 

No 

43  1. Reconnect all previously disconnected fuse, 

relay or harness connector(s). 

2.  Turn OFF the ignition for 30 seconds. 
3.  Turn ON the ignition, with the engine OFF. 
4.  Turn ON the blower motor switch. 
Does the blower motor turn ON and operate 
correctly? 

 

Go to Char 1 of 2 

Step 4 

Refer to Applicable 
Diagnostic Chart in 

Heating & Air 

Conditioning 

Section 

 

 

Engine Control System (4JH1)  6E-255 

Symptoms – Engine Controls  

Symptoms – Engine Controls 

 

 

Important Preliminary Inspections Before Starting 
Perform Diagnostic System Check – Engine Controls
before using the symptom tables, and verify that all of
the following are true: 

•  The engine control module (ECM) and malfunction

indicator lamp (MIL) are operating correctly. 

•  There are no diagnostic trouble codes (DTCs)

stored, or a DTC exists but without the MIL. 

•  The scan tool data is within the normal operating

range. Refer to scan tool Data List in this section.

•  Verify the customer concern and locate the correct

symptom in the table of contents. Inspect the items
indicated under that symptom. 

Visual and Physical Inspection 
Several of the symptom procedures ask for careful
visual and physical inspection. This step is extremely
important. The visual and physical inspection can lead
to correcting a problem without further inspections, and
can save valuable time. Ensure that:  

•  The ECM grounds are clean, tight, and in their

proper location. 

•  The vacuum hoses are not split or kinked, and

properly connected. Inspect thoroughly for any
type of leak or restriction. 

•  The mass air flow (MAF) sensor is properly

installed. The arrows on the plastic portion of the
sensor must point toward the engine. 

•  The air intake ducts are not collapsed or damaged.
•  There are no leaks at the MAF sensor, any

connections or intake manifold sealing surfaces. 

•  The engine harness wiring and terminals are

properly connected and are not pinched or cut. 

Intermittent 
Important: 
Inspect for improper installation of electrical
components if an intermittent condition exists. Inspect
for aftermarket add-on electrical equipment devices,
lights, and cellular phones. Verify that no aftermarket
equipment is connected to the keyword 2000 serial data
circuit. If you cannot locate an intermittent condition, a
cellular phone communication signal may cause the
condition. 
Important: 
The problem may or may not turn ON the MIL or store a 
DTC. 
 

 

Faulty electrical connections or wiring cause most
intermittent problems. Perform a careful visual and
physical inspection of the suspect connectors for the
following conditions: 

•  Improperly mated connector halves 
•  Terminals that are not seated 
•  Terminals that are damaged or improperly formed

Reform or replace connector terminals in the problem
circuit in order to ensure proper contact tension.
Remove the terminal from the connector body in order
to inspect for poor terminal wire connection. 
Road test the vehicle with the DMM connected to the
suspected circuit. An abnormal reading that occurs
when the malfunction occurs is a good indication that
there is a malfunction in the circuit being monitored. 
Use the scan tool in order to help detect intermittent 
conditions. Useful features of the scan tool include the
following: 

•  Trigger the Snapshot feature in order to capture 

and store engine parameters when the malfunction 
occurs. Review this stored information in order to 
see the specific running conditions that caused the
malfunction. 

•  Use the Plot Function on the scan tool in order to 

plot selected data parameters. Review this stored 
information to aid in locating an intermittent 
problem. Refer to the scan tool Users Guide for 
more information. 

Important: 
If the intermittent condition exists as a start and then
stall, test for DTCs relating to the vehicle theft deterrent
system. Test for improper installation of electrical
options such as lights, cellular phones, etc. 
Any of the following may cause an intermittent MIL with
no stored DTC: 

•  The ECM grounds are loose or dirty. Refer to 

Engine Controls Schematics. 

•  The MIL circuit intermittently shorted to ground. 
• Electrical system interference caused by a 

malfunctioning relay, ECM driven solenoid, or 
switch. The electrical component can cause a 
sharp electrical surge. Normally, the problem will 
occur when the malfunctioning component is 
operating. 

• There is an open diode across the A/C 

compressor clutch or any other open diodes. 

 
 

6E-256  Engine Control System (4JH1) 

Important:  
The following symptom tables contain groups of
possible causes for each symptom. The order of these
procedures is not important. If the scan tool readings do
not indicate the problems, then proceed in a logical
order, easiest to check or most likely to cause first. In
order to determine if a specific vehicle is using a
particular system or component, refer to Engine
Controls Schematics for an application. 
Use the following tables when diagnosing a symptom
complaint: 

• Intermittent 

Conditions 

•  Hard Start  
•  Rough, Unstable, or Incorrect Idle and Stalling 
•  Cuts Out, Misses 
• Surge/Chuggles 
•  Lack of Power, Sluggishness, or Sponginess 
•  Hesitation, Sag, Stumble 
•  Fuel Knock/Combustion Noise 
•  Poor Fuel Economy 
•  Excessive Smoke (Black Smoke) 
•  Excessive Smoke (White Smoke) 

 

 

 
 

Intermittent Conditions 

Checks Action 

DEFINITION:The problem is not currently present but is indicated in DTC History. 
OR 
There is a customer complaint, but the symptom cannot currently be duplicated, if the problem is not DTC related. 
Preliminary Checks  

• Refer to Symptoms – Engine Controls before starting. 

Harness/Connector 

Many intermittent open or shorted circuits are affected by harness/connector 
movement that is caused by vibration, engine torque, bumps/rough pavement, etc. 
Test for this type of condition by performing the applicable procedure from the 
following list: 
• Move related connectors and wiring while monitoring the appropriate scan tool data. 
• Move related connectors and wiring with the component commanded ON, and OFF, 

with the scan tool. Observe the component operation. 

• With the engine running, move related connectors and wiring while monitoring 

engine operation. 
If harness or connector movement affects the data displayed, component/system 
operation, or engine operation, inspect and repair the harness/connections as 
necessary. 
Refer to Electrical Connections or Wiring. 

Engine Control System (4JH1)  6E-257 

Checks Action 

Electrical Connections or Wiring 

Poor electrical connections, terminal tension or wiring problems cause most 
intermittent. To perform the following inspections: 
• Inspect for poor mating of the connector halves, or terminals improperly seated in the 

connector body.  

• Inspect for improperly formed or damaged terminals. Test for poor terminal tension.  
• Inspect for poor terminal to wire connections including terminals crimped over 

insulation. This requires removing the terminal from the connector body.  

• Inspect for corrosion/water intrusion. Pierced or damaged insulation can allow 

moisture to enter the wiring. The conductor can corrode inside the insulation, with 
little visible evidence. Look for swollen and stiff sections of wire in the suspect 
circuits.  

• Inspect for wires that are broken inside the insulation.  
• Inspect the harness for pinched, cut or rubbed through wiring.  
• Ensure that the wiring does not come in contact with hot exhaust components.  

Control Module Power and Grounds 
Component Power and Grounds 

Poor power or ground connections can cause widely varying symptoms. 
• Test all control module power supply circuits. Many vehicles have multiple circuits 

supplying power to the control module. Other components in the system may have 
separate power supply circuits that may also need to be tested. Inspect connections 
at the module/component connectors, fuses, and any intermediate connections 
between the power source and the module/component. A test lamp or a DMM may 
indicate that voltage is present, but neither tests the ability of the circuit to carry 
sufficient current. Ensure that the circuit can carry the current necessary to operate 
the component. 

• Test all control module ground and system ground circuits. The control module may 

have multiple ground circuits. Other components in the system may have separate 
grounds that may also need to be tested. Inspect grounds for clean and tight 
connections at the grounding point. Inspect the connections at the component and in 
splice packs, where applicable. Ensure that the circuit can carry the current 
necessary to operate the component. 

Temperature Sensitivity 

• An intermittent condition may occur when a component/connection reaches normal 

operating temperature. The condition may occur only when the 
component/connection is cold, or only when the component/connection is hot.  

• If the intermittent is related to heat, review the data for a relationship with the 

following:  

- High ambient temperatures 
- Under hood/engine generated heat 
- Circuit generated heat due to a poor connection, or high electrical load 
- Higher than normal load conditions, towing, etc. 

• If the intermittent is related to cold, review the data for the following:  

- Low ambient temperatures–In extremely low temperatures, ice may form in a 

connection or component. Test for water intrusion. 

- The condition only occurs on a cold start. 
- The condition goes away when the vehicle warms up. 

• Information from the customer may help to determine if the trouble follows a pattern 

that is temperature related.