Isuzu N-Series. Manual - part 769

Engine Control System (4JH1) 6E-127

Turn OFF the ignition.

Disconnect the MAF sensor harness
connector.

Inspect for an intermittent, for a poor
connection and corrosion at the harness
connector of the MAF sensor (pin 3 of J-182
connector).

Disconnect the engine control module (ECM)
harness connector.

Inspect for an intermittent, for a poor
connection and corrosion on each MAF
sensor circuit at the harness connector of the
ECM (pin 92 of B-233 connector).

Test for high resistance on each MAF sensor
circuit.

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-128 Engine Control System (4JH1)

P0400 (Symptom Code 8) (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 a short to battery or
ignition voltage 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 high voltage condition

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

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.

Test Description
The number below refers to the step number on the
diagnostic table.
3. If the control circuit of the EGR solenoid valve
between the ECM and the solenoid valve is normal, the
control circuit voltage low DTC P0400 (Symptom Code
4) will set.

DTC P0400 (Symptom Code 8) (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 warm up (allow engine
coolant temperature to reach at least 75

°C

[167

°F]).

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.

Start the engine.

Monitor the DTC Information with the Tech 2.

Does the DTC P0400 (Symptom Code 4) set, but
not DTC P0400 (Symptom Code 8)?

—

Go to Step 5

Go to Step 4

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 a short to battery or
ignition voltage.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

Engine Control System (4JH1) 6E-129

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

Did you complete the replacement?

—

Go to Step 7

—

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 7

—

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]).

Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 8

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-130 Engine Control System (4JH1)

P0500 (Symptom Code 1, A) (Flash Code 24)

Circuit Description
The vehicle speed sensor (VSS) is used by the engine
control module (ECM) and speedometer, which
generates a speed signal from the transmission output
shaft. The VSS has the following circuits.

• Ignition voltage feed circuit
• VSS signal circuit
• VSS low reference circuit

The VSS uses a hall effect element. It interacts with
the magnetic field created by the rotating magnet and
outputs square wave pulse signal. The ECM calculates
the vehicle speed by the VSS. If the ECM detects VSS
signals are generated with high frequencies, this DTC
will set.

Condition for Running the DTC

• The ignition switch is ON.

Condition for Setting the DTC

• The ECM detects that the vehicle speed is higher

than 190 km/h (119 MPH) for 5 seconds.
(Symptom Code 1)

• The ECM detects that the vehicle speed sensor

signal frequency is too high for 0.6 seconds.
(Symptom Code A)

Action Taken When the DTC Sets

• The ECM does not illuminate the malfunction

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

• The ECM uses a vehicle speed substitution of 5

km/h (3 MPH) for engine control.

Condition for Clearing the DTC

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the Tech 2.

Diagnostic Aids

• Electrical or magnetic interference may affect

intermittent condition.

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

DTC P0500 (Symptom Code 1, A) (Flash Code 24)
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

Inspect all of the circuits going to the vehicle
speed sensor (VSS) for the following:

• Routed too closely to fuel injection

solenoid wiring or components

• Routed too closely to after-market add-

on electrical equipment

• Routed too closely to solenoids, relays,

and motors

If you find incorrect routing, correct the
harness routing.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 3

Turn OFF the ignition.

Disconnect the VSS harness connector.

Inspect for an intermittent and for poor
connections at the harness connector of the
VSS (pins 1, 2 and 3 of J-32 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 4

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