Isuzu N-Series. Manual - part 703

6E-234    Engine Control System (4HK1) 

10

1.

Remove the cylinder head cover. Refer to Fuel
Injector Replacement in this section.

2.

Inspect the fuel injector harness for loose
injector terminal nuts, objects touching injector
terminals.

3.

Inspect for an intermittent and for a poor
connection at the in-line harness connector
(pins 1 and 4 of H-126 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 11

11

1.

Disconnect the fuel injector harness from the
cylinder number 1 and number 4 fuel injectors
(E-138 and E-141 connector).

2.

Measure the insulation resistance between
cylinder number 1 fuel injector terminals and a
known good ground.

3.

Measure the insulation resistance between
cylinder number 4 fuel injector terminals and a
known good ground.

Is the insulation resistance more than the specified
value on each measurement?

1 M

Ω

Go to Step 12

Go to Step 13

12

Repair or replace the injector harness. Refer to
Fuel Injector Replacement in this section.

Did you complete the repair or replace?

—

Go to Step 15

—

13

Important:
Replacement injector must be programmed.

Replace the appropriate fuel injector that was less
insulation resistance found at Step 11. Refer to
Fuel Injector Replacement / Fuel Injector ID Code
Data Programming in this section.

Did you complete the replacement?

—

Go to Step 15

—

14

Important:
Replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module
(ECM) Replacement / Fuel Injector ID Code Data
Programming in this section.

Did you complete the replacement?

—

Go to Step 15

—

15

1.

Reconnect all previously disconnected
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 16

16

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

No

 Engine Control System (4HK1)    6E-235

P1262 (Flash Code 159)

Circuit Description
The common 2 fuel injector drive circuit is a high-
voltage supply which drives injectors for cylinder
number 2 and 3 in conjunction with the engine control
module (ECM) grounding the fuel injector control
circuit. The ECM also supplies battery voltage to the
fuel injector solenoid control circuit to allow for fault
detection. If the common 2 fuel injector drive circuit is
open circuit, short to ground or short to voltage, this
DTC will set. Or, if the cylinder number 2 or number 3
fuel injector solenoid control circuit is shorted to
ground, this DTC will also set.

Condition for Running the DTC

• DTC P0612 is not set.
• The ignition switch is ON.
• The battery voltage is more than 18 volts.
• The engine is running.

Condition for Setting the DTC
Either of following condition is met:

• The ECM detects that the common 2 fuel injector

drive circuit is open circuit, shorted to ground or
shorted to voltage during engine rotations.

• The ECM detects that the cylinder number 2 or

number 3 fuel injector solenoid coil control circuit is
shorted to ground during engine rotations.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM limits accelerator control range.
• The ECM inhibits pilot injection.

Condition for Clearing the MIL / DTC

• The ECM turns OFF the MIL and exhaust brake

indicator lamp 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

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

DTC P1262 (Flash Code 159)
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

2

Important:
If DTC P0202 or P0203 is also set, diagnose that
DTC first.

1.

Install the Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

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

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic 

Aids

3

1.

Turn OFF the ignition.

2.

Disconnect the in-line harness connector (H-
125) from the cylinder head cover case.

3.

Connect a DMM between the cylinder number
2 fuel injector control circuit (pin 6 of H-125
female side connector) and a known good
ground.

4.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage more than the specified value?

12.0 volt

Go to Step 4

Go to Step 6

6E-236    Engine Control System (4HK1) 

4

1.

Connect a test lamp between the common 2
fuel injector drive circuit (pin 2 or 3 of H-125
female side connector) and a known good
ground.

2.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 7

Go to Step 5

5

1.

Connect a test lamp between the common 2
fuel injector drive circuit (pins 2 or 3 of H-125
female side connector) and battery voltage.

2.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 8

Go to Step 9

6

1.

Test the cylinder number 2 or number 3 fuel
injector solenoid control circuit between the
engine control module (ECM) and the in-line
harness connector (H-125 connector) for a
short to ground.

• Cylinder #2: Between pin 118 of E-111

connector and 6 of H-125 connector

• Cylinder #3: Between pin 120 of E-111

connector and 7 of H-125 connector

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

7

1.

Test the common 2 fuel injector drive circuit
between the ECM (pin 116 of E-111
connector) and the in-line harness connector
(pins 2 and 3 of H-125 connector) for a short
to battery or ignition voltage.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

8

1.

Test the common 2 fuel injector drive circuit
between the ECM (pin 116 of E-111
connector) and the in-line harness connector
(pins 2 and 3 of H-125 connector) for a short
to ground.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

9

1.

Inspect for an intermittent and for a poor
connection at the in-line harness connector
(pins 2 and 3 of H-125 connector).

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for a poor
connection on the common 2 fuel injector
drive circuit at the harness connector of the
ECM (pin 116 of E-111 connector).

4.

Inspect for an open circuit or high resistance
on the common 2 fuel injector drive circuit
between the ECM (pin 116 of E-111
connector) and the in-line harness connector
(pins 2 and 3 of H-125 connector).

5.

Repair the connection(s) or circuit(s) as
necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 10

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-237

10

1.

Remove the cylinder head cover. Refer to Fuel
Injector Replacement in this section.

2.

Inspect the fuel injector harness for loose
injector terminal nuts, objects touching injector
terminals.

3.

Inspect for an intermittent and for a poor
connection at the in-line harness connector
(pins 2 and 3 of H-126 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 11

11

1.

Disconnect the fuel injector harness from the
cylinder number 2 and number 3 fuel injectors
(E-139 and E-140 connector).

2.

Measure the insulation resistance between
cylinder number 2 fuel injector terminals and a
known good ground.

3.

Measure the insulation resistance between
cylinder number 3 fuel injector terminals and a
known good ground.

Is the insulation resistance more than the specified
value on each measurement?

1 M

Ω

Go to Step 12

Go to Step 13

12

Repair or replace the injector harness. Refer to
Fuel Injector Replacement in this section.

Did you complete the repair or replace?

—

Go to Step 15

—

13

Important:
Replacement injector must be programmed.

Replace the appropriate fuel injector that was less
insulation resistance found at Step 11. Refer to
Fuel Injector Replacement / Fuel Injector ID Code
Data Programming in this section.

Did you complete the replacement?

—

Go to Step 15

—

14

Important:
Replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module
(ECM) Replacement / Fuel Injector ID Code Data
Programming in this section.

Did you complete the replacement?

—

Go to Step 15

—

15

1.

Reconnect all previously disconnected
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 16

16

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

No