Dtc P0091 Or P0092 (Flash Code 247) - Isuzu N 2008 Series Workshop Manual

1A-80 Engine Control System (4JJ1)

DTC P0091 or P0092 (Flash Code 247)

Circuit Description
The fuel rail pressure (FRP) regulator is installed to the
fuel supply pump and controls the suction fuel quantity
into the fuel rail. The FRP regulator is fully opened in
the normal state and larger drive current results in
smaller opening. The ECM calculates desired fuel rail
pressure and fuel flow rate and it compares the
calculated desired fuel rail pressure to the actual value
to determine the FRP regulator position. When the
actual fuel rail pressure is higher than the desired
value, the FRP regulator is closed to decease the flow
rate. If the ECM detects an excessively low or high FRP
regulator solenoid feedback current, DTC P0091 or
P0092 will set.
Condition for Running the DTC
• DTCs P060B is not set.
• The battery voltage is between 18 to 32 volts.
• The ignition switch is ON.
Condition for Setting the DTC
• The ECM detects that the FRP regulator feedback
current is less than 50 mA, or more than 1000 mA
below the desired current. (DTC P0091)
• The ECM detects that the FRP regulator feedback
current is more than 2400 mA, or more than
1000 mA over the desired current. (DTC P0092)
Circuit/ System Testing DTC P0091 or P0092
Step
Did you perform the Diagnostic System Check -
1 Engine Controls?
1. Install a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF.
2
4. Monitor the DTC Information with a scan tool.
Does the DTC fail this ignition?
Observe the Fuel Rail Pressure (FRP) Regulator
Feedback Current parameter with a scan tool.
3
Does the scan tool indicate more than the specified
value?
Does the scan tool indicate more than the specified
4
value at Step 3?
1. Turn OFF the ignition.
2. Disconnect
connector.
3. Connect a test lamp between the high side
5
circuit (pin 1 of E17) and a known good
ground.
4. Turn ON the ignition, with the engine OFF.
Does the test lamp illuminate?
Action
the FRP regulator harness
Action Taken When the DTC Sets
• The ECM illuminates the MIL when the diagnostic
runs and fails. Refer to DTC Type Definitions for
Action Taken When the DTC Sets - Type A.
• The ECM limits fuel injection quantity.
• The ECM inhibits pre injection.
• The ECM inhibits EGR control.
Condition for Clearing the DTC
• Refer to DTC Type Definitions for Condition for
Clearing the MIL/ DTC - Type A.
Diagnostic Aids
• If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.
Test Description
The number below refers to the step number on the
Circuit/ System Testing.
7. If the FRP regulator high side circuit is shorted to
voltage, engine stalls and will not start.
8. If the FRP regulator low side circuit is shorted to
ground, this DTC may not set. This will cause engine
stall or no engine start.
Connector End View Reference: Engine Controls
Connector End Views or ECM Connector End Views
Value(s) Yes
—
Go to Step 2
—
Go to Step 3
300 mA
Go to Step 4
900 mA
Go to Step 7
—
Go to Step 6
No
Go to Diagnostic
System Check -
Engine Controls
Go to Diagnostic
Aids
Go to Step 5
Go to Step 8
Go to Step 9