Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 38

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–147

Condition for setting the DTC and action taken when the DTC sets

Circuit Description

The ECM is calculates an injection quantity and an
injection timing using the various sensors. And the PSG
controls the high pressure solenoid valve depending on
programmed pump map data.

The signal of desired injection quantity and actual injec-
tion quantify are exchanged via the CAN-bus between
the PSG and ECM.
If the relation of engine speed signal and doubled pump
camshaft speed signal excessively large, DTC P0251
(Symptom Code 7) will be stored.
If the CAN high or low circuit is defected, DTC P0251
(Symptom Code E) will be stored.

Diagnostic Aids

An intermittent may be caused by the following:

• Poor connections.

• Misrouted harness.

• Rubbed through wire insulation.

• Broken wire inside the insulation.
Check for the following conditions:

• Poor connection at ECM and PSG-Inspect harness

connectors for backed out terminals, improper
mating, broken locks, improperly formed or damaged
terminals, and poor terminal to wire connection.

• Damaged harness-Inspect the wiring harness for

damage. If the harness appears to be OK, observe
the “Injection Quantity” display on the Tech2 while
moving connectors and wiring harness related to the
sensor.

Diagnostic Trouble Code (DTC) P0251 (Symptom Code 6) (Flash Code 53)

Injection Pump Malfunction

Flash

Code

Symptom

Code

MIL

DTC Name

DTC Setting Condition

Fail-Safe (Back Up)

P0251

Injection Pump Malfunction

1. No pump camshaft speed

sensor error.

2. High pressure solenoid

valve control pulse width
does not match with
desired fuel injection quan-
tity.

1. MAB (fuel cutoff solenoid

valve) is operated.

2. Desired injection quantity

becomes 0mg/strk.

Injection Pump Malfunction

1. No pump camshaft speed

sensor error.

2. No CKP sensor error.
3. Difference of engine speed

and doubled pump cam-
shaft speed is more than
720rpm (4JA1-TC) or
690rpm (4JH1-TC).

Injection Pump Malfunction

No pump map programmed in
the PSG (pump control unit)
or PSG malfunction.

Injection Pump Malfunction

EEPROM or A/D converter
malfunction in the PSG (pump
control unit).

Fuel injection quantity is
reduced.

Injection Pump Malfunction

PSG (pump control unit) rec-
ognized high pressure sole-
noid valve drive circuit error.

No fail-safe function.

Injection Pump Malfunction

PSG (pump control unit) could
not measure the high pres-
sure solenoid valve drive volt-
age.

Injection Pump Malfunction

ECM could not accept PSG
(pump control unit) message.

1. MAB (fuel cutoff solenoid

valve) is operated.

2. Desired injection quantity

becomes 0mg/strk.

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to Step 2

Go to On Board

Diagnostic

(OBD) System

Check

6E–148

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

1. Connect the Tech 2.

2. Review and record the failure information.

3. Select “F0: Read DTC Infor As Stored By ECU” in

“F0: Diagnostic Trouble Codes”.

Is the DTC P0251 (Symptom Code 6) stored as
“Present Failure”?

—

Go to Step 3

Refer to

Diagnostic Aids

and Go to Step

1. Using the Tech 2, ignition “On” and engine “Off”.

2. Select “F1: Clear DTC Information” in “F0:

Diagnostic Trouble Codes” with the Tech 2 and
clear the DTC information.

3. Operate the vehicle and monitor the “F0: Read

DTC Infor As Stored By ECU” in the “F0:
Diagnostic Trouble Codes”.

Was the DTC P0251 (Symptom Code 6) stored in this
ignition cycle?

—

Go to Step 4

Refer to

Diagnostic Aids

Replace the injection pump assembly.
Is the action complete?

—

Verify repair

—

Step

Action

Value(s)

Yes

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–149

Diagnostic Trouble Code (DTC) P0251 (Symptom Code 7) (Flash Code 53)

Injection Pump Malfunction

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to Step 2

Go to On Board

Diagnostic

(OBD) System

Check

1. Connect the Tech 2.

2. Review and record the failure information.

3. Select “F0: Read DTC Infor As Stored By ECU” in

“F0: Diagnostic Trouble Codes”.

Is the DTC P0251 (Symptom Code 7) stored as
“Present Failure”?

—

Go to Step 3

Refer to

Diagnostic Aids

and Go to Step

1. Using the Tech 2, ignition “On” and engine “Off”.

2. Select “F1: Clear DTC Information” in “F0:

Diagnostic Trouble Codes” with the Tech 2 and
clear the DTC information.

3. Operate the vehicle and monitor the “F0: Read

DTC Infor As Stored By ECU” in the “F0:
Diagnostic Trouble Codes”.

Was the DTC P0251 (Symptom Code 7) stored in this
ignition cycle?

—

Go to Step 4

Refer to

Diagnostic Aids

and Go to Step

Was the DTC P0335 (Symptom Code B), P0335
(Symptom Code D) or P1335 (Symptom Code A)
stored at the same time?

—

Go to DTC

Chart P0335

(Symptom

Code B)

(Symptom

Code D) or

P1335

(Symptom

Code A)

Go to Step 5

Check for poor/faulty connection at the ECM or PSG
(pump control unit) connector. If a poor/faulty
connection is found, repair the faulty terminal.
Was the problem found?

—

Verify repair

Go to Step 6

C-57(B)

E-6

6E–150

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

If a oscilloscope is available, monitor the CKP sensor
output signal. Does the oscilloscope indicate correct
wave form?

—

Go to Step 13

Not available:

Go to Step 7

Fixed at low: Go

to Step 7

Fixed at High:

Go to Step 8

Step

Action

Value(s)

Yes

CKP Sensor Output Reference Wave Form

→

Measurement Terminal: 91 (+) 1 (-)
Measurement Scale: 5.0V/div

2.0ms/div

Measurement Condition: Engine speed at 2000rpm

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