Isuzu N-Series. Service manual - part 688

6E-174    Engine Control System (4HK1) 

P0381 (Flash Code 67)

Circuit Description
The glow indicator lamp is located on the instrument
panel cluster (IPC). The glow control system is
operated when the engine coolant temperature is low,
which allows easier engine starting. If the ignition
switch is turned ON when the engine coolant
temperature is low, the engine control module (ECM)
illuminates the glow indicator lamp and turns ON the
glow plugs. After a fixed time passes, the ECM turns
OFF the glow indicator lamp and the glow plugs. The
ECM monitors the glow indicator lamp control circuit for
conditions that are incorrect for the commanded state
of the glow indicator lamp. For example, a failure
condition exists if the ECM detects low voltage when
the glow indicator lamp is commanded OFF, or high
voltage when the glow indicator lamp is commanded
ON. If the ECM detects an improper voltage on the
glow indicator control circuit, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.
• The ignition voltage is more than 18 volts.

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

• The ECM detects a low voltage condition on the

glow indicator lamp control circuit when the
indicator is commanded OFF for longer than 5
seconds.

• The ECM detects a high voltage condition on the

glow indicator lamp control circuit when the
indicator is commanded ON for longer than 5
seconds.

Action Taken When the DTC Sets

• The ECM does not illuminate the malfunction

indicator lamp (MIL) when the diagnostic runs and
fails.

Condition for Clearing the DTC

• 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 P0381 (Flash Code 67)
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

1.

Verify whether the instrument cluster is
operational. If the instrument panel cluster
(IPC) is completely inoperative, refer to
Diagnostic System Check.

2.

Turn OFF the ignition for 30 seconds.

3.

Disconnect the engine coolant temperature
(ECT) sensor harness connector in order to
gain glow ON time long enough.

4.

Turn ON the ignition for 20 seconds while
observing 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.

Inspect the Meter (10A) fuse in the glove box.

Is the Meter (10A) fuse open?

—

Go to Step 4

Go to Step 5

4

Replace the Meter (10A) fuse. If the fuse continues
to open, repair the short to ground on one of the
circuits that is fed by the Meter (10A) fuse or
replace the shorted attached component fed by the
Meter (10A) fuse.

Did you complete the repair?

—

Go to Step 19

—

 Engine Control System (4HK1)    6E-175

5

1.

Turn OFF the ignition.

2.

Disconnect the engine control module (ECM)
J-191 harness connector.

3.

Turn ON the ignition, with the engine OFF.

Is the glow indicator lamp OFF?

—

Go to Step 6

Go to Step 13

6

1.

Remove the Meter (10A) fuse that supplies
voltage to the glow indicator lamp.

2.

Turn ON the ignition, with the engine OFF.

3.

Measure the voltage from the glow indicator
lamp control circuit in the ECM harness
connector (pin 11 of J-191 connector) to a
good ground.

Is the voltage less than the specified value?

1 volt

Go to Step 7

Go to Step 14

7

1.

Turn OFF the ignition.

2.

Install the Meter (10A) fuse that supplies
ignition voltage to the glow indicator lamp.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a 3-amp fused jumper wire between
the glow indicator lamp control circuit of the
ECM harness connector (pin 11 of J-191
connector) and a known good ground.

Is the glow indicator lamp illuminated?

—

Go to Step 12

Go to Step 8

8

1.

Turn OFF the ignition.

2.

Remove the IPC.

3.

Remove the glow indicator lamp bulb from the
IPC.

Is the glow indicator bulb burned out?

—

Go to Step 16

Go to Step 9

9

1.

Connect a test lamp between the glow
indicator lamp ignition voltage circuit of the
IPC harness connector (pin 18 of B-51
connector) and a known good ground.

2.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 10

Go to Step 15

10

1.

Test the glow indicator lamp control circuit
between the ECM (pin 11 of J-191 connector)
and the IPC (pin 15 of B-52 connector) for an
open circuit or high resistance.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 11

11

1.

Turn OFF the ignition.

2.

Inspect for an intermittent and for poor
connections at the harness connector of the
IPC (pins 18 of B-51 and 15 of B-52
connector).

3.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 17

Step

Action

Value(s)

Yes

No

6E-176    Engine Control System (4HK1) 

12

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for a poor
connection on the glow indicator lamp control
circuit at the harness connector of the ECM
(pin 11 of J-191 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 18

13

Repair the short to ground on the control circuit of
the glow indicator lamp between the ECM (pin 11 of
J-191 connector) and the IPC (pin 15 of B-52
connector).

Did you complete the repair?

—

Go to Step 19

—

14

Repair the short to battery or ignition voltage on the
control circuit of the glow indicator lamp between
the ECM (pin 11 of J-191 connector) and the IPC
(pin 15 of B-52 connector).

Did you complete the repair?

—

Go to Step 19

—

15

Repair the open or high resistance on the ignition
voltage circuit of the glow indicator lamp between
the Meter (10A) fuse and the IPC (pin 18 of B-51
connector).

Did you complete the repair?

—

Go to Step 19

—

16

Replace the glow indicator lamp bulb.

Did you compete the replacement?

—

Go to Step 19

—

17

Repair or replace the IPC.

Did you complete the repair or replacement?

—

Go to Step 19

—

18

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

—

19

1.

Reconnect all previously disconnected fuse or
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Disconnect the ECT sensor harness
connector in order to gain glow ON time long
enough.

5.

Turn ON the ignition for 20 seconds while
observing the DTC Information with the Tech
2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 20

20

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-177

P0485 (Flash Code 44)

Circuit Description
The exhaust gas recirculation (EGR) valve position
sensor is installed on the EGR valve body together with
the EGR valve control motor. The EGR valve position
sensor changes output voltage according to EGR valve
position. The EGR position sensor has the following
circuits.

• 5 volts reference circuit
• Low reference circuit
• EGR valve position sensor signal circuit

The engine control module (ECM) supplies 5 volts to
the EGR valve position sensor on the 5 volts reference
circuit. The ECM also provides a ground on the low
reference circuit. The EGR valve position sensor
provides a signal to the ECM on the EGR valve position
signal circuit, which is relative to the position changes
of the EGR valve. The ECM monitors the EGR position
sensor signals for voltage outside the normal range of
the EGR position. If the ECM detects an excessively
low EGR valve position signal voltage, this DTC will
set.

Condition for Running the DTC

• DTCs P1630 and P1635 are not set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.

Condition for Setting the DTC

• The ECM detects that the EGR valve position

sensor signal voltage is less than 0.1 volts for 5
seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM inhibits EGR valve control.

Condition for Clearing the MIL / DTC

• The ECM turns OFF the MIL when the key is

cycled after a current DTC clears.

• A current DTC clears when the diagnostic runs and

does not fail.

• 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 P0485 (Flash Code 44)
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

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.

Is DTC P1635 also set?

—

Go to DTC P1635

Go to Step 3

3

1.

Start the engine.

2.

Observe the EGR Position Sensor parameter
with the Tech 2.

Is the EGR Position Sensor parameter less than
the specified value?

0.1 volts

Go to Step 4

Go to Diagnostic 

Aids

4

1.

Turn OFF the ignition.

2.

Disconnect the EGR valve harness connector.

3.

Connect a DMM between the 5 volts reference
circuit of the EGR position sensor harness (pin
1 of E-94 connector) and a known good
ground.

4.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage more than the specified value?

4.5 volts

Go to Step 5

Go to Step 6