Isuzu N-Series. Manual - part 699
6E-218 Engine Control System (4HK1)
P1095 (Flash Code 225)
Description
The common rail fuel system is comprised of two fuel
pressure sections: a suction side between the fuel tank
and the fuel supply pump and a high-pressure side
between the fuel supply pump and the fuel injectors.
Fuel is drawn from the fuel tank via a feed pump and
then pumped into the fuel rail by two plungers, all of
which are internal to the fuel supply pump. This high
pressure is regulated by the engine control module
(ECM) using the fuel rail pressure (FRP) regulator
dependant upon values from the FRP sensor attached
to the fuel rail. In case of fuel rail overpressure, a
pressure limiter valve threaded into the fuel rail will
open to release overpressure and return fuel back to
the fuel tank.
If the ECM detects that the fuel rail pressure went
excessively high, then sharply decreased, this DTC will
set indicating high fuel pressure, which activated the
pressure limiter valve.
Condition for Running the DTC
• DTCs P0192, P0193, P1630 and P1635 are not
set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.
Condition for Setting the DTC
• The ECM detects that the FRP sensor signal
voltage drops quickly from more than 3.7 volts to
less than 2.3 volts, and then the differential fuel rail
pressure is more than -30 MPa (4,350 psi).
Action Taken When the DTC Sets
• The ECM illuminates the malfunction indicator
lamp (MIL) when the diagnostic runs and fails.
Condition for Clearing the MIL / DTC
• The ECM turns OFF the MIL when the key is
cycled after a current DTC clears.
• A current DTC clears when the diagnostic runs and
does not fail at next driving cycle.
• A history DTC clears after 20 consecutive driving
cycles without a fault. Or clear with the Tech 2 or
accelerator pedal operation.
Diagnostic Aid
• An intermittently sticking FRP regulator may have
allowed the fuel pressure to become high enough
to open the pressure limiter valve.
• Normal FRP Sensor readings on the Tech 2 with
the engine running in neutral at idle is around 1.4 –
1.6 volts.
• A skewed FRP sensor value (shifted to a higher
pressure) can set this DTC. The FRP Sensor on
the Tech 2 should read 0.9 – 1.0 volt with the key
ON and engine OFF after the engine has stopped
running for a minimum of 2 minutes.
Notice:
• The fuel system from the fuel tank(s) to the fuel
supply pump is under a slight vacuum with the
engine running. As a result, air can enter the fuel
system if these connections are not tight or if there
is a crack in one of the fuel hoses. Air in the fuel
system will cause fuel rail pressure fluctuations
especially at high engine speed and load, which
may set this DTC.
Notice:
• If the fuel tank is empty or near empty, air might be
allowed to go into the fuel system. With air in the
fuel system, smooth flow of fuel into the supply
pump is interrupted and this DTC may set. Perform
bleeding of fuel system after refilling.
Test Description
The numbers below refers to the step number on the
diagnostic table.
6. This step checks for a fuel restriction by determining
if a high vacuum is being pulled on the fuel system
during normal operation.
7. This step checks for an air leak on the suction side of
the fuel system by determining if a vacuum can be
pulled when a fuel line is plugged.
DTC P1095 (Flash Code 225)
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