Isuzu N-Series. Manual - part 702

6E-230 Engine Control System (4HK1)

Test the 5 volts reference circuit between the
engine control module (ECM) (pin 42 of J-191
connector) and the idle up sensor harness (pin
3 of B-281 connector) for an open circuit or
high resistance.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 16

Test the signal circuit between the ECM (pin
66 of J-191 connector) and the idle up sensor
(pin 2 of B-281 connector) for the following
conditions:

• An open circuit
• A short to ground
• A short to the low reference circuit
• High resistance

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 16

Important:
The idle up sensor may be damaged if the sensor
signal circuit is shorted to a voltage source.

Test the signal circuit between the ECM (pin
66 of J-191 connector) and the idle up sensor
(pin 2 of B-281 connector) for the following
conditions:

• A short to battery or ignition voltage
• A short to any 5 volts reference

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 18

Test the low reference circuit between the
ECM (pin 41 of J-191 connector) and the idle
up sensor (pin 1 of B-281 connector) for an
open circuit or high resistance.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 16

Turn OFF the ignition.

Disconnect the idle up sensor harness
connector.

Inspect for an intermittent and for poor
connections at the harness connector of the
idle up sensor (pins 1, 2 and 3 of B-281
connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 17

Turn OFF the ignition.

Disconnect the ECM harness connector.

Inspect for an intermittent and for poor
connections on the idle up sensor circuits at
the harness connector of the ECM (pins 41,
42 and 66 of J-191 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 18

Step

Action

Value(s)

Yes

Engine Control System (4HK1) 6E-231

Replace the idle up sensor. Refer to Idle Up Sensor
Replacement in this section.

Did you complete the replacement?

—

Go to Step 19

—

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 19

—

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine.

Fully turn the idle up sensor to lowest position
(full counterclockwise direction) and highest
position (full clock wise direction) while
observing the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter within the
specified valve?

0.2 – 4.8 volts

Go to Step 20

Go to Step 3

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-232 Engine Control System (4HK1)

P1261 (Flash Code 158)

Circuit Description
The common 1 fuel injector drive circuit is a high-
voltage supply which drives injectors for cylinder
number 1 and 4 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 1 fuel injector drive circuit is
open circuit, short to ground or short to voltage, this
DTC will set. Or, if the cylinder number 1 or number 4
fuel injector solenoid control circuit is shorted to
ground, this DTC will also set.

Condition for Running the DTC

• DTC P0611 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 1 fuel injector

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

• The ECM detects that the cylinder number 1 or

number 4 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 P1261 (Flash Code 158)
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

Important:
If DTC P0201 or P0204 is also set, diagnose that
DTC first.

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine.

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

Turn OFF the ignition.

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

Connect a DMM between the cylinder number
1 fuel injector control circuit (pin 5 of H-125
female side connector) and a known good
ground.

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

Engine Control System (4HK1) 6E-233

Connect a test lamp between the common 1
fuel injector drive circuit (pin 1 or 4 of H-125
female side connector) and a known good
ground.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 7

Go to Step 5

Connect a test lamp between the common 1
fuel injector drive circuit (pins 1 or 4 of H-125
female side connector) and battery voltage.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 8

Go to Step 9

Test the cylinder number 1 or number 4 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 #1: Between pin 119 of E-111

connector and 5 of H-125 connector

• Cylinder #4: Between pin 117 of E-111

connector and 8 of H-125 connector

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

Test the common 1 fuel injector drive circuit
between the ECM (pin 121 of E-111
connector) and the in-line harness connector
(pins 1 and 4 of H-125 connector) for a short
to battery or ignition voltage.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

Test the common 1 fuel injector drive circuit
between the ECM (pin 121 of E-111
connector) and the in-line harness connector
(pins 1 and 4 of H-125 connector) for a short
to ground.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

Inspect for an intermittent and for a poor
connection at the in-line harness connector
(pins 1 and 4 of H-125 connector).

Disconnect the ECM harness connector.

Inspect for an intermittent and for a poor
connection on the common 1 fuel injector
drive circuit at the harness connector of the
ECM (pin 121 of E-111 connector).

Inspect for an open circuit or high resistance
on the common 1 fuel injector drive circuit
between the ECM (pin 121 of E-111
connector) and the in-line harness connector
(pins 1 and 4 of H-125 connector).

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

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