Isuzu 4HL1 Workshop Manual page 201

Circuit Description
The pump pressure is controlled with the common rail
pressure. The common rail pressure is detected by the
common rail pressure sensor and sent to the ECM. The
ECM calculates desired common rail pressure and
pump flow rate from the data sent from sensors and
compares these calculations with the actual common
rail pressure to determine the SCV position. When the
actual pressure is lower than the desired pressure, the
SCV is opened to increase the pump flow rate. When
the actual pressure is higher than the desired pressure,
the SCV is closed to decrease the pump flow rate.
DTC227 will be set when the common rail pressures is
excessively low.
Major Faulty Event
• Engine stall
Conditions for Setting the DTC
The fuel leak after the fuel filter exceeds the threshold.
Action Taken When the DTC Sets
• After the DTC is set, the ECM will illuminate the
CHECK ENGINE lamp (MIL).
• The ECM prepares for engine shutdown.
Conditions for Clearing MIL/DTC
When the system fails and the DTC is stored to the
ECM, even repairing the faulty portion will not clear the
DTC from the memory. To clear the DTC, conduct the
following steps.
25 6 8 27 26
CKP CMP
Sensor Sensor
63 66 6764
69 68
ITP EGR Valve
Sensor Position
Sensor
1. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
2. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
3. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
4. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
5. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
6. After the above operations are properly completed,
the CHECK ENGINE lamp (MIL) illuminates for 3
seconds to report the memory is cleared.
7. Turn off the starter switch. Wait for 5 seconds and
turn on the starter switch again.
When Tech 2 has been connected to the vehicle, the
DTC can be cleared through the memory clear
operation with Tech 2.
Diagnostic Aids
When the air mixes into the fuel system, the fuel
pressure (common rail pressure) may read incorrect
value. If air bleed resolves the fault, the possible cause
is the air mixing into fuel system.
Engine Control System 1A-199
ECM
(Engine
Control
Module)
Common
Rail
Pressure
Sensor
LNW21AMF006901-X