Isuzu N-Series. Manual - part 767

Engine Control System (4JH1) 6E-119

P0400 (Symptom Code 3) (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 lower than desired MAF amount, this DTC
will set. This indicates excessive 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 lower than the desired MAF for 60 seconds.
This indicates excessive 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.

DTC P0400 (Symptom Code 3) (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-120 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 vacuum hose

and ventilation hose that is damaged or
kinked.

• An EGR valve is stuck open.
• Any type of restriction in the exhaust

system.

• Air leakage around the MAF sensor or

debris in the sensor housing.

• Air leaking around any of the air induction

tubing between the MAF sensor and
intake manifold.

• Turbine shaft binding causing lower

turbocharger shaft spinning speeds.
Refer to the Turbocharger in Engine
Mechanical section for diagnosis.

• Restricted air cleaner element, restricted

or collapsed air tubing between the air
cleaner and the turbocharger.

• 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, skewed or slow 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

Step

Action

Value(s)

Yes

Engine Control System (4JH1) 6E-121

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

Turn OFF the ignition.

Disconnect the MAF sensor harness
connector.

Inspect for an intermittent, for poor
connections and corrosion at the harness
connector of the MAF sensor (pins 2, 4 and 5
of J-182 connector).

Disconnect the engine control module (ECM)
harness connector.

Inspect for an intermittent, for poor
connections and corrosion on each MAF
sensor circuit at the harness connector of the
ECM (pins 83 and 88 of B-233 connector).

Test for high resistance on each MAF sensor
circuit.

Test the MAF sensor signal circuit short to
intake air temperature (IAT) sensor signal.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 8

Replace the EGR valve. Refer to EGR Valve
Replacement in engine mechanical section.

Did you complete the replacement?

—

Go to Step 10

—

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

Did you complete the replacement?

—

Go to Step 10

—

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with 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]) while observing the MAF Sensor

parameter with the Tech 2.

Does the MAF Sensor parameter follow the
Desired MAF parameter within 50 mg/strk?

—

Go to Step 11

Go to Step 2

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-122 Engine Control System (4JH1)

P0400 (Symptom Code 4) (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 that an open circuit
or short to ground on the EGR solenoid valve control
circuit, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.

Condition for Setting the DTC

• The ECM detects that the low voltage condition on

the EGR solenoid valve control circuit for longer
than 3 seconds when the solenoid valve is
commanded OFF.

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.

DTC P0400 (Symptom Code 4) (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.

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 EGR control solenoid valve
harness connector.

Connect a test lamp between the voltage feed
circuit of the EGR control solenoid valve
harness (pin 1 of J-105 connector) and a
known good ground.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 4

Go to Step 6

Connect a test lamp between the control
circuit of the EGR solenoid valve harness (pin
2 of J-105 connector) and battery voltage.

Perform the EGR Solenoid Valve test with the
Tech 2.

Command the EGR Solenoid Valve ON with
the Tech 2.

Does the test lamp illuminate when commanded
ON with the Tech 2?

—

Go to Step 5

Go to Step 7

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