Isuzu KB P190. Manual — part 295

6E-146 Engine Control System (4JH1)

DTC 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 850

hPa and 1100 hPa.

• The intake air temperature (IAT) is between 15°C

(59°F) and 100°C (212°F).

• The ECT is between 35°C (95°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 scan tool.

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

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 scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine and let idle for 30 seconds.
4. Monitor the Diagnostic Trouble Code (DTC)

Information with the scan tool.

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

3

1. Install the scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine and warm up (allow engine

coolant temperature to reach at least 60°C
[140°F]).

4. Perform the EGR Solenoid Valve test with the

scan tool.

5. Command the EGR Solenoid Valve ON and OFF

with the scan tool 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

Engine Control System (4JH1) 6E-147

Step Action

Value(s)

Yes

No

4

1. Turn OFF the ignition.
2. Inspect for the following conditions:

• An EGR valve control vacuum hose is

damaged or kinked.

• EGR solenoid valve vacuum hoses are

damaged or kinked.

• EGR solenoid valve ventilation is damaged.
• 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
wipe off.

• Contaminated, skewed or slow MAF

sensor.

3. Repair or replace as necessary.
Did you find and correct the condition?



Go to Step 10

Go to Step 5

5

1. Turn OFF the ignition.
2. Disconnect the EGR valve control vacuum hose

from the EGR valve.

3. Connect a hand-held vacuum pump (5-8840-

0279-0/J-23738-A) to the disconnected vacuum
hose.

4. Start the engine and let engine idle.
5. Perform the EGR Solenoid Valve test with the

scan tool.

6. Command the EGR Solenoid Valve ON and OFF

with the scan tool.

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

6

1. Turn OFF the ignition.
2. Disconnect the hand-held vacuum pump from the

vacuum hose.

3. Connect the hand-held vacuum pump to the

vacuum port of EGR valve.

4. Start the engine and let engine idle.
5. 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

6E-148 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

7

1. Turn OFF the ignition.
2. Disconnect the MAF sensor harness connector.
3. Inspect for an intermittent, for poor connections

and corrosion at the harness connector of the
MAF sensor (pins 2, 4 and 5 of C-116
connector).

4. Disconnect the engine control module (ECM)

harness connector.

5. 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
C-57 connector).

6. Test for high resistance on each MAF sensor

circuit.

7. Test the MAF sensor signal circuit short to intake

air temperature (IAT) sensor signal.

8. Repair the circuit(s) as necessary.
Did you find and correct the condition?



Go to Step 10

Go to Step 8

8

Replace the EGR valve. Refer to EGR Valve
Replacement in engine mechanical section.
Did you complete the replacement?



Go to Step 10



9

Replace the EGR solenoid valve. Refer to EGR
Solenoid Valve Replacement in this section.
Did you complete the replacement?



Go to Step 10



10

1. Reconnect all previously disconnected harness

connector(s).

2. Clear the DTCs with the scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine and warm up (allow engine

coolant temperature to reach at least 60°C
[140°F]) while observing the MAF Sensor
parameter with the scan tool.

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



Go to Step 11

Go to Step 2

11

Observe the DTC Information with the scan tool.
Are there any DTCs that you have not diagnosed?



Go to Diagnostic

Trouble Code (DTC)

List System

OK

Engine Control System (4JH1) 6E-149

DTC 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 scan tool.

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

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 scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Monitor the Diagnostic Trouble Code (DTC)

Information with the scan tool.

Does the DTC fail this ignition?



Go to Step 3

Go to Diagnostic

Aids

3

1. Turn OFF the ignition.
2. Inspect the ECM (10A) fuse (EB-4) in the engine

room fuse block.

Is the ECM (10A) fuse (EB-4) open?



Go to Step 4

Go to Step 5

4

Replace the ECM (10A) fuse (EB-4). If the fuse
continues to open, repair the short to ground on one
of the circuits that fed by the ECM (10A) fuse (EB-4)
or replace the shorted attached component fed by
the ECM (10A) fuse (EB-4).
Did you complete the repair?



Go to Step 15



5

1. Turn OFF the ignition.
2. Disconnect the EGR control solenoid valve

harness connector.

3. Connect a test lamp between the voltage feed

circuit of the EGR control solenoid valve harness
(pin 1 of C-115 connector) and a known good
ground.

4. Turn ON the ignition, with the engine OFF.
Does the test lamp illuminate?



Go to Step 6

Go to Step 8