Isuzu N-Series. Manual - part 761

Engine Control System (4JH1) 6E-95

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine and let idle for 30 seconds.

Accelerate the engine between idle and
W.O.T. (accelerator pedal full travel) many
times while observing the DTC Information
with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 5

Observe the DTC Information with the Tech 2.

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic

Trouble Code (DTC)

List

System OK

Step

Action

Value(s)

Yes

6E-96 Engine Control System (4JH1)

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 800
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 Tech 2.

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

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic

System Check –

Engine Controls

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine. If the engine does not start,
crank over the engine.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

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

Start the engine.

Monitor the DTC Information with the Tech 2.

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

Engine Control System (4JH1) 6E-97

Observe the Engine Speed parameter with the
Tech 2.

Accelerate the engine between idle and
W.O.T. (accelerator pedal full travel) many
times while observing the Tech 2.

Does the Engine Speed parameter indicate correct
engine speed?

—

Go to Step 9

Go to Step 5

Inspect the crankshaft position (CKP) sensor
for tightness.

Remove the CKP sensor and check for
damage, metal particles on magnet and for
flywheel circumference damage.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 6

Turn OFF the ignition.

Disconnect the CKP sensor harness
connector.

Inspect for an intermittent, for poor
connections and corrosion on the CKP sensor
terminal (pins 1, 2 and 3 of J-183 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 7

Turn OFF the ignition.

Disconnect the fuel injection pump control unit
(PCU) harness connector.

Inspect for an intermittent, for a poor
connection and corrosion on the CKP sensor
signal input at the harness connector of the
PCU (pin 8 of E-110 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 8

Turn OFF the ignition.

Disconnect the engine control module (ECM)
harness connector.

Inspect for an intermittent, for poor
connections and corrosion on at the harness
connector of the ECM (pins 90, 91, 98 and
101 of B-233 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 9

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 10

—

Step

Action

Value(s)

Yes

6E-98 Engine Control System (4JH1)

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine.

Accelerate the engine between idle and
W.O.T. (accelerator pedal full travel) many
times while observing the DTC Information
with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 2

Go to Step 11

Observe the DTC Information with the Tech 2.

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic

Trouble Code (DTC)

List

System OK

Step

Action

Value(s)

Yes

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