Isuzu N-Series. Manual - part 768

Engine Control System (4JH1) 6E-123

Command the EGR Solenoid Valve OFF with the
Tech 2.

Does the test lamp continuously illuminate same as
Step 4 when commanded OFF with the Tech 2 (the
test lamp slightly illuminates if the circuit is normal
when commanded OFF)?

—

Go to Step 8

Go to Step 9

Repair the open circuit or high resistance on the
voltage feed circuit between the ECM main relay
(pin 5 of X-14 connector) and the EGR solenoid
valve (pin 1 of J-105 connector).

Did you complete the repair?

—

Go to Step 13

—

Test the control circuit between the engine
control module (ECM) (pin 97 of B-233
connector) and the EGR solenoid valve (pin 2
of J-105 connector) for an open circuit or high
resistance.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10

Test the control circuit between the ECM (pin
97 of B-233 connector) and the EGR solenoid
valve (pin 2 of J-105 connector) for a short to
ground.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

Turn OFF the ignition.

Disconnect the EGR solenoid valve harness
connector.

Inspect for an intermittent and for poor
connections at the harness connector of the
EGR solenoid valve (pins 1 and 2 of J-105
connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

Turn OFF the ignition.

Disconnect the ECM harness connector.

Inspect for an intermittent and for a poor
connection on the EGR solenoid valve control
circuit at the harness connector of the ECM
(pin 97 of B-233 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

Replace the EGR solenoid valve. Refer to EGR
Solenoid Valve Replacement in this section.

Did you complete the replacement?

—

Go to Step 13

—

Important:
Replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.

Did you complete the replacement?

—

Go to Step 13

—

Step

Action

Value(s)

Yes

6E-124 Engine Control System (4JH1)

Reconnect all previously disconnected or
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine.

Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 14

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

Engine Control System (4JH1) 6E-125

P0400 (Symptom Code 5) (Flash Code 32)

Circuit Description
The engine control module (ECM) controls the exhaust
gas recirculation (EGR) flow amount based on the
engine speed, engine coolant temperature, intake air
temperature, barometric pressure and fuel injection
quantity. The ECM controls the EGR valve by
controlling the EGR solenoid valve. The mass air flow
(MAF) sensor monitors EGR gas flow amount. An
expected MAF amount should be detected while the
engine running. If the ECM detects the actual MAF
amount is higher than desired MAF amount, this DTC
will set. This indicates insufficient amount of EGR gas
flow.

Condition for Running the DTC

• The ignition switch is ON.
• The engine is running.
• The barometric pressure (BARO) is between 880

hPa and 1100 hPa.

• The intake air temperature (IAT) is between 16

°C

(61

°F) and 34°C (93°F).

• The ECT is between 70

°C (158°F) and 100°C

(211

°F).

Condition for Setting the DTC

• The ECM detects that the MAF amount is 150 mg/

strk higher than the desired MAF for 60 seconds.
This indicates insufficient amount of EGR flow.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM limits fuel injection quantity.

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

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• A sticking or intermittently sticking the EGR valve

will cause this DTC to set.

• Misrouted vacuum hoses will cause this DTC to

set.

• A vacuum pump problem will cause this DTC to

set.

DTC P0400 (Symptom Code 5) (Flash Code 32)
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 and let idle for 30 seconds.

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

Is DTC P0100 (Symptom Code 7, 9, B or C) or
P0400 (Symptom Code 4 or 8) set?

—

Go to Applicable

DTC

Go to Step 3

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine and warm up (allow engine
coolant temperature to reach at least 75

°C

[167

°F]).

Perform the EGR Solenoid Valve test with the
Tech 2.

Command the EGR Solenoid Valve ON and
OFF with the Tech 2 while observing the Mass
Air Flow (MAF) Sensor parameter.

Does the MAF Sensor parameter decrease by at
least 200 mg/strk within 2 seconds when the EGR
Solenoid Valve is commanded ON?

—

Go to Diagnostic

Aids

Go to Step 4

6E-126 Engine Control System (4JH1)

Turn OFF the ignition.

Inspect for the following conditions:

• An EGR valve control vacuum hose is

damaged or kinked.

• An EGR solenoid valve control vacuum

hose and ventilation hose that is
damaged or kinked.

• An EGR valve is stuck close.
• Restricted or collapsed EGR passage

between the exhaust manifold and EGR
valve.

• A vacuum hose from the vacuum pump is

damaged or kinked.

• A vacuum pump is damaged.
• Oil in the air tubing causing an incorrect

MAF sensor signal. When there is
adhesion of oil, inside of the tubing,
intercooler and turbocharger needs to be
wiped off.

• Contaminated or skewed MAF sensor.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 5

Turn OFF the ignition.

Disconnect the EGR valve control vacuum
hose from the EGR valve.

Connect a hand-held vacuum pump (5-8840-
0279-0/J-23738-A) to the disconnected
vacuum hose.

Start the engine and let engine idle.

Perform the EGR Solenoid Valve test with the
Tech 2.

Command the EGR Solenoid Valve ON and
OFF with the Tech 2.

Does the hand-held vacuum pump indicate more
than 50 cmHg (20 inHg) when commanding the ON
and less than 10 cmHg (4 inHg) when commanding
OFF?

—

Go to Step 6

Go to Step 9

Turn OFF the ignition.

Disconnect the hand-held vacuum pump from
the vacuum hose.

Connect the hand-held vacuum pump to the
vacuum port of EGR valve.

Start the engine and let engine idle.

Apply vacuum pressure to the EGR valve
while observing the MAF Sensor parameter.

Does the MAF Sensor parameter decrease by at
least 200 mg/strk when the vacuum pressure is
applied?

—

Go to Diagnostic

Aids

Go to Step 7

Step

Action

Value(s)

Yes

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