Isuzu N-Series. Manual - part 762
Engine Control System (4JH1) 6E-99
P0251 (Symptom Code 9, A, B, D) (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 shutoff.)
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.
Condition for Running the DTC
• The ignition switch is ON.
Condition for Setting the DTC
• The PCU detects internal fuel injection pump
control maps are not programmed during self-test.
(Symptom Code 9)
• The PCU detects internal EEPROM or A/D
converter is failed during self-test. (Symptom
Code A)
• The PCU detects that the fuel injection solenoid
valve drive circuit is failed during self-test.
(Symptom Code B)
• The PCU detects that the fuel injection solenoid
valve drive circuit voltage level is abnormal during
self-test. (Symptom Code D)
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. (Symptom Code 9)
• The ECM limits fuel injection quantity. (Symptom
Code A)
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 Tech 2.
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 9, A, B, D) (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 Tech 2.
2.
Turn OFF the ignition for 30 seconds.
3.
Turn ON the igniton, with the engine OFF.
4.
Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.
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
—