2007 ISUZU KB P190 engine

6E-42 Engine Control System (4JH1)
Scan Tool Does Not Communicate with Keyword 2000 Device
Circuit Description
The engine control module (ECM), transmission control
module (TCM) and anti-theft (keyless entry) control unit
(ACU) all communicate with the scan tool over the
Keyword 2000 serial data link. However, the ECM and
fuel injection pump control unit (PCU) communicates
with each other over the controller area network (CAN)
link. The CAN link is not used for communication with
the scan tool and is shared only between the ECM and
PCU.
Diagnostic Aids
The following conditions will cause a loss of Keyword
2000 serial data communication between the TCM and
EHCU or between the scan tool and any control module:

• A Keyword 2000 serial data circuit open.
• A Keyword 2000 serial data circuit shorted to
ground.
• A Keyword 2000 serial data circuit shorted to
voltage.
•
An internal condition within a module or connector
on the Keyword 2000 serial data circuit, that causes
a short to voltage or ground to the Keyword 2000
serial data circuit.
• Open ground circuit (pin 5) at the DLC.

Scan tool Does Not Communicate with Keyword
2000 Device
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Step Action Value(s) Yes No
1 Did you perform the Diagnostic System Check-
Engine Controls? 
Go to Step 2 Go to Diagnostic
System Check-
Engine Controls
2 1. Install the scan tool. 2. Turn ON the ignition, with the engine OFF.
3. Attempt to communicate with the listed control modules. • Engine control module (ECM)
• Transmission control module (TCM) (A/T
only)
• Electronic hydraulic control unit (EHCU)
Does the scan tool communicate with all the listed
control modules? 

Go to Step 3 Go to Step 8
3 Does the scan tool communicate with the ECM? 
Go to Step 4 Go to Lost
Communication with The ECM
4 Does the scan tool communicate with the TCM?

Go to Step 5 Go to Diagnostic
System Check Transmission Control
5 Does the scan tool communicate with the EHCU? 
Go to Step 6 Go to Diagnostic
System Brake
6 Test the Keyword 2000 serial data circuit for an intermittently short to ground or intermittently short to
voltage. Then, test the Keyword 2000 serial data
circuit for an intermittently open (based on which
control module did not communicate) at the
connection in the circuit.
Did you find and correct the condition? 

Go to Step 15 System OK
7 Test the data link connector (DLC) ground circuit at terminal 5 for an open circuit or poor connection.
Did you find and correct the condition? 

Go to Step 15 Go to Step 8

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ISUZU KB P190 2007

Engine Control System (4JH1) 6E-43
Step Action Value(s) Yes No
8 1. Turn OFF the ignition.
2. Disconnect the ECM C-56 and C-57 harness connectors.
3. Turn ON the ignition, with the engine OFF.
4. Attempt to communicate with the TCM and EHCU.
Does the scan tool communicate with the TCM and
EHCU? 

Go to Step 12 Go to Step 9
9 1. Turn OFF the ignition. 2. Reconnect the ECM C-56 and C-57 harness connectors.
3. Disconnect the TCM A and B harness connectors.
4. Turn ON the ignition, with the engine OFF.
5. Attempt to communicate with the ECM and EHCU.
Does the scan tool communicate with the ECM and
EHCU? 

Go to Step 13 Go to Step 10
10 1. Turn OFF the ignition. 2. Reconnect the TCM A and B harness connectors.
3. Disconnect the EHCU C-67 harness connectors.
4. Turn ON the ignition, with the engine OFF.
5. Attempt to communicate with the ECM and TCM.
Does the scan tool communicate with the ECM and
TCM? 

Go to Step 14 Go to Step 11
11 Repair the short to ground or short to voltage on the Keyword 2000 serial data circuit between the DLC
and ECM, TCM and EHCU.
Did you complete the repair? 

Go to Step 15 
12 Important: Replacement ECM must be
programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.
Did you complete the replacement? 

Go to Step 15 
13 Important: Replacement TCM must be
programmed.
Replace the TCM. Refer to Transmission Control
Module (TCM) Replacement in the transmission
section.
Did you complete the replacement? 

Go to Step 15 
14 Replace the EHCU. Refer to Electronic Hydraulic
Control Unit in the anti-lock brake system section.
Did you complete the replacement? 

Go to Step 15 
15 Attempt to communicate with the ECM, TCM and
EHCU.
Does the scan tool communicate with the ECM, TCM
and EHCU? 

System OK Go to Step 2


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ISUZU KB P190 2007

6E-44 Engine Control System (4JH1)
Lost Communication with The Engine Control Module (ECM)
Circuit Description
The engine control module (ECM), transmission control
module (TCM) and electronic hydraulic control unit
(EHCU) all communicate with the scan tool over the
Keyword 2000 serial data link. However, the ECM and
fuel injection pump control unit (PCU) communicates
with each other over the controller area network (CAN)
link. The CAN link is not used for communication with
the scan tool and is shared only between the ECM and
PCU.


Lost Communication with The Engine Control
Module (ECM)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Step Action Value(s) Yes No
1 Did you perform the Diagnostic System Check-
Engine Controls? 
Go to Step 2 Go to Diagnostic
System Check-
Engine Controls
2 Attempt to establish engine control module (ECM) communications with the scan tool.
Does the ECM communicate with the scan tool? 
Go to Intermittent
Conditions Go to Step 3
3 Check the ECM C-56 and C-57 connectors for poor connections.
Did you find and correct the condition? 

Go to Step 17 Go to Step 4
4 Check the electronic hydraulic control unit (EHCU)
C-67 connector for poor connection.
Did you find and correct the condition? 

Go to Step 17 Go to Step 5
5 1. Turn ON the ignition, with the engine OFF. 2. Check the ECM (30A) (SFB-4), ECM (10A) fuse (EB-4) and Engine (15A) fuse (C-6).Replace and
retest if open. If any fuse continues to open,
check for a short to ground on each circuit fed by
that fuse.
3. Turn OFF the ignition.
4. Disconnect the ECM C-56 harness connector.
5. Turn ON the ignition, with the engine OFF.
6. Connect a test lamp to ground and check for voltage at the ignition voltage supply circuit at the
ECM (pin 39 of C-56 connector).
Does the test lamp illuminate? 

Go to Step 6 Go to Step 14
6 1. Turn OFF the ignition. 2. Connect a DMM between the Keyword 2000 serial data circuit at the ECM (pin 35 of C-56
connector) and the EHCU (pin 11 of C-67
connector).
3. Test the circuits for an open circuit or high resistance.
4. Repair the circuit(s) as necessary.
Did you find and correct the condition? 

Go to Step 17 Go to Step 7
7 1. Turn OFF the ignition. 2. Connect a DMM between the Keyword 2000 serial data circuit at the EHCU (pin 11 of C-67
connector) and the DLC (pin 7 of B-58
connector).
3. Test the circuits for an open circuit or high resistance.
4. Repair the circuit(s) as necessary.
Did you find and correct the condition? 

Go to Step 17 Go to Step 8

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ISUZU KB P190 2007

Engine Control System (4JH1) 6E-45
Step Action Value(s) Yes No
8 Important: An open in a ground circuit at the ECM
will not cause a loss of communication.
1. Check ECM ground for corrosion and tightness.
2. Clean or tighten grounds as necessary.
Did you find and correct the condition? 

Go to Step 17 Go to Step 9
9 1. Turn OFF the ignition. 2. Reconnect the ECM harness connector if previously disconnected.
3. Turn ON the ignition, with the engine OFF.
4. Replace the ECM main relay with the tail relay or replace with a known good relay.
5. Attempt to establish scan tool communications with the ECM.
Does the ECM communicate with the scan tool? 

Go to Step 15 Go to Step 10
10 1. Turn OFF the ignition. 2. Remove the ECM main relay.
3. Turn ON the ignition, with the engine OFF.
4. Using a test lamp, check for battery voltage at both of the battery voltage supply circuits to the
ECM main relay (pins 2 and 5 of X-12
connector).
5. Repair the open in the circuit(s) as necessary.
Did you find and correct the condition? 

Go to Step 17 Go to Step 11
11 1. Reinstall the ECM main relay. 2. Turn the ignition ON and OFF while listening or feeling for the ECM main relay click. W ait 2
seconds between transitions.
Does the ECM main relay click when the ignition is
turned ON or OFF? 

Go to Step 13 Go to Step 12
12 Repair the ECM main relay control circuit between the ECM main relay (pin 4 of X-12 connector) and
the ECM (pin 58 of C-56 connector) for the following
conditions: • An open circuit
• A short to battery or ignition voltage
• High resistance or a poor connection at
both the ECM and ECM main relay
Did you find and correct the condition? 

Go to Step 17 Go to Step 16
13 1. Check ECM main relay voltage supply circuit to the ECM between the ECM main relay (pin 1 of
X-12 connector) and the ECM (pin 3 of C-56
connector) for the following conditions: • An open circuit
• High resistance or a poor connection at the
ECM and ECM main relay
2. Repair the circuit(s) as necessary.
Did you find and correct the condition? 

Go to Step 17 Go to Step 16
14 Repair the open in the ignition voltage circuit to the ECM.
Did you complete the repair? 

Go to Step 17 
15 Replace the ECM main relay.
Did you complete the replacement? 

Go to Step 17 
16 Important: Replacement ECM must be
programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.
Did you complete the replacement? 

Go to Step 17 

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ISUZU KB P190 2007

6E-46 Engine Control System (4JH1)
Step Action Value(s) Yes No
17 1. Turn OFF the ignition.
2. Reconnect all disconnected connectors.
3. Turn the ignition ON with the engine OFF.
4. Attempt to establish scan tool communications with the ECM.
Does the scan tool communicate with the ECM? 

System OK Go to Step 3



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ISUZU KB P190 2007

Engine Control System (4JH1) 6E-47
Engine Cranks but Does Not Run
Description
The Engine Cranks but Does Not Run diagnostic table
is an organized approach to identifying a condition that
causes an engine to not start. The diagnostic table
directs the service technician to the appropriate system
diagnosis. The diagnostic table assumes the following
conditions are met:
• The battery is completely charged and terminals
are cleaned and tight.
• The engine cranking speed is normal.
• There is adequate fuel in the fuel tank.
• There is no fuel leak in the fuel line.
• There is no air in the fuel line.
• Filters (Air, Fuel) are clean.
• Fuse and slow blow fuse are normal.

Diagnostic Aids
• If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.



Step Action Value(s) Yes No
1 Did you perform the Diagnostic System Check-
Engine Controls? 
Go to Step 2 Go to Diagnostic
System Check-
Engine Controls
2 1. Install the scan tool. 2. Turn OFF the ignition for 30 seconds.
3. Crank the engine for specified amount of time.
4. Monitor the Diagnostic Trouble Code (DTC) Information with the scan tool.
Does the scan tool display any DTCs that failed this
ignition? 15 seconds
Go to Diagnostic
Trouble Code (DTC) List Go to Step 3
3 1. Check for normal readings at key up for the
following inputs and output: Refer to the scan
tool Data List or a known good vehicle to
determine normal values. • System Voltage
• Engine Coolant Temperature (ECT)
• Intake Air Temperature (IAT)
• Mass Air Flow (MAF) Sensor
• Barometric Pressure
• Desired Injection Quantity
2. Repair or replace as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 4

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ISUZU KB P190 2007

6E-48 Engine Control System (4JH1)
Step Action Value(s) Yes No
4 1. Inspect the high pressure side between the fuel
injection pump and the fuel injection nozzles for
fuel leakage. The following components may
contain an external leak. • Fuel injection pump
• Fuel injection pump control unit (PCU)
• Fuel injection solenoid valve
• Timing control valve (TCV)
• Constant pressure valve (CPV)
• Fuel pipe between the fuel injection pump
and fuel injection nozzles
• Each fuel pipe sleeve nuts
• Each fuel pipe connectors
• Each gaskets
Notice: Fuel may leak into the engine from the fuel
injection pump. In such case, the engine oil level will
rise. Inspect for fuel leakage into the engine oil.
2. Repair any fuel system leaks as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 5
5 1. Turn OFF the ignition. 2. Check the fuel system line connections between the fuel tank and the fuel injection pump for
tightness and all fuel hoses for cuts, cracks and
for the use of proper clamps.
3. Pump the priming pump on the fuel filter until it becomes firm. If there is a leak on the suction
side of the fuel system between the priming
pump and the fuel injection pump, the priming
pump will not build up sufficient firmness and fuel
leakage may occur.
4. Repair or replace as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 6
6 1. Remove the fuel hose that connects to the fuel injection pump suction side.
2. Remove the fuel pipe connector that connects to the fuel injection pump suction side.
3. Inspect the eye bolt for any type of restriction or collapsed gauze filter.
Notice: If any type of restriction found, check for a
condition that causes contaminated fuel, such as the
customer is using an aftermarket fuel filter or
extended maintenance interval.Also inspect fuel
waxing or icing that is caused by an incorrect fuel
type used in winter season or water intrusion in the
fuel system.
4. Repair or replace as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 7

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ISUZU KB P190 2007

Engine Control System (4JH1) 6E-49
Step Action Value(s) Yes No
7 1. Disconnect the fuel hose that connects to the
fuel injection pump suction side. In order to
measure the discharged fuel amount, put the
hose into a bottle or a container.
2. Pump the priming pump on the fuel filter.
Notice: If there is a leak on the suction side of the
fuel system, the fuel from the disconnected hose will
not flow out sufficiently and fuel leakage may occur.
Also if there is a restriction on the suction side of the
fuel system, the fuel from the disconnected hose will
not flow out sufficiently that is most likely caused by
clogged fuel filter or kinked fuel hose or pipe.
3. Draw fuel from the fuel tank at the fuel line (as close to the fuel tank as possible) going to the
fuel pickup tube to verify a clean stream of fuel
comes out (use the hand-held vacuum pump 5-
8840-0279-0/J-23738-A with a clear hose or
equivalent). This will ensure the fuel pickup tube
is not cracked drawing air into the fuel line.
4. Repair any fuel system leaks and restrictions as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 8
8 1. Other possible causes for the no-start condition: • Fuel injection pump mechanical timing
incorrect
• Flywheel installed incorrectly causing the
crankshaft position (CKP) sensor to be
incorrectly timed to the engine. Disconnect
sensor and attempt to start engine to verify.
• Heavily restricted intake, exhaust or
catalytic converter plugged solid
• Poor engine compression
• W ater or gasoline contamination in fuel
2. Repair or replace as necessary.
Did you find and correct the condition? 

Go to Step 10 Go to Step 9
9 Important: The fuel injection pump must be timed to
the engine.
Replace the fuel injection pump. Refer to Fuel
Injection Pump Replacement in engine mechanical
section.
Did you complete the replacement? 

Go to Step 10 
10 1. Reconnect all previously disconnected harness
connector(s).
2. Turn OFF the ignition for 30 seconds.
3. Attempt to start the engine.
Does the engine start and continue to run? 

Go to Step 11 Go to Step 2
11 Observe the DTC Information with the scan tool. Are there any DTCs that you have not diagnosed?  Go to Diagnostic
Trouble Code (DTC) List System OK

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ISUZU KB P190 2007