Isuzu KB P190. Service manual — part 289

6E-122 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

4

1. Test the control circuit between the engine

control module (ECM) (pin 96 of C-57 connector)
and the turbocharger solenoid valve (pin 2 of C-
123 connector) for a short to battery or ignition
voltage.

2. Repair the circuit(s) as necessary.
Did you find and correct the condition?



Go to Step 7

Go to Step 6

5

Replace the turbocharger solenoid valve. Refer to
Turbocharger Solenoid Valve Replacement in this
section.
Did you complete the replacement?



Go to Step 7



6

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 7



7

1. Reconnect all previously disconnected harness

connector(s).

2. Clear the DTCs with the scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Monitor the DTC Information with the scan tool.
Did the DTC fail this ignition?



Go to Step 3

Go to Step 8

8

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

Engine Control System (4JH1) 6E-123

DTC P0251 (Symptom Code 6) (Flash Code 53)

Circuit Description
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.
The fuel injection solenoid valve is installed to the fuel
injection pump rear side. The fuel injection event is
determined by this solenoid ON/OFF command. The
fuel injection solenoid valve cuts the fuel when the
engine shutoff (ESO) solenoid valve is commanded
shutoff from the PCU. (The fuel injection solenoid valve
and engine shutoff (ESO) solenoid valve is same part. It
calls ESO solenoid valve when fuel is shut off.) When
the ignition switch is turned OFF or commanded from
fail-safe action, the ESO solenoid valve is commanded
shutoff to stop the engine running. If the PCU detects
that the fuel injection solenoid valve is operated when
the desired injection quantity from the ECM is 0 mg/strk,
this DTC will set.

Condition for Running the DTC

• The fuel injection pump CMP sensor signal is

generated.

• The CAN communication between the ECM and

PCU is normal.

Condition for Setting the DTC

• The PCU detects that the fuel injection solenoid

valve is operated when the desired fuel injection
quantity is commanded 0 mg/strk.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM cuts fuel injection.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the scan tool.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Notice:

• Fuel injection solenoid valve is internal to the fuel

injection pump assembly.

• PCU is part of the fuel injection pump assembly.

DTC P0251 (Symptom Code 6) (Flash Code 53)

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. Start the engine and let idle for 30 seconds.
4. Accelerate the engine between idle and W.O.T.

(accelerator pedal full travel) many times while
observing the Diagnostic Trouble Code (DTC)
Information with the scan tool.

Does the DTC fail this ignition?



Go to Step 3

Go to Step 4

3

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 4



6E-124 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

4

1. Clear the DTCs with the scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine and let idle for 30 seconds.
4. Accelerate the engine between idle and W.O.T.

(accelerator pedal full travel) many times while
observing the DTC Information with the scan
tool.

Did the DTC fail this ignition?



Go to Step 3

Go to Step 5

5

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

Engine Control System (4JH1) 6E-125

DTC P0251 (Symptom Code 7) (Flash Code 53)

Circuit Description
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. The PCU also
compares the engine speed signal sent from the ECM
and the fuel injection pump speed. If the PCU detects
that the doubled fuel injection pump speed is
excessively lower than engine speed, this DTC will set.
Condition for Running the DTC

• The fuel injection pump CMP sensor signal is

generated.

• The crankshaft position (CKP) sensor signal is

generated.

• The engine speed is higher than 500 RPM.

Condition for Setting the DTC

• The PCU detects that the doubled fuel injection

pump speed is lower than engine speed by 690
RPM for longer than 0.2 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM cuts fuel injection.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the scan tool.

Diagnostic Aids

• Electrical or magnetic interference may affect

intermittent condition.

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Notice:

• Fuel injection pump CMP sensor is internal to the

fuel injection pump assembly.

• PCU is part of the fuel injection pump assembly.

DTC P0251 (Symptom Code 7) (Flash Code 53)
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 OFF the ignition for 30 seconds.
3. Start the engine. If the engine does not start,

crank over the engine.

4. Monitor the Diagnostic Trouble Code (DTC)

Information with the scan tool.

Is DTC P0335 (Symptom Code B, D or E), P1335
(Symptom Code A) or P1345 (Symptom Code A)
set?



Go to Applicable

DTC

Go to Step 3

3

1. Start the engine.
2. Monitor the DTC Information with the scan tool.
3. Accelerate the engine between idle and W.O.T.

(accelerator pedal full travel) many times.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic

Aids