Isuzu N-Series. Service manual - part 711

6E-266 Engine Control System (4HK1)

P1634 (Flash Code 55)

Circuit Description
The engine control module (ECM) provides 5 volts
reference voltage through the reference circuit 4 to the
boost pressure sensor. The ECM also has ability to
provide 5 volts reference voltage through the reference
circuit 3. But it is not used. The 5 volts reference
circuits 3 and 4 are independent of each other outside
of the ECM, but are bussed together inside the ECM.
Therefore, a short circuit condition on one sensor 5
volts reference circuit may affect the entire 5 volt
reference circuit 3 and 4. The ECM monitors the
voltage on the 5 volts reference circuit 3 and 4. If the
ECM detects the voltage is excessively low or high, this
DTC and DTC P1633 will also set.

Condition for Running the DTC

• DTC P1630 is not set.
• The ignition switch is ON.
• The battery voltage is between 16 – 32 volts.

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

• The ECM detects that the 5 volts reference circuit

3 or 4 voltage is less than 4.5 volts.

• The ECM detects that the 5 volts reference circuit

3 or 4 voltage is more than 5.5 volts.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM limits accelerator control range.
• The ECM inhibits pilot injection.
• 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 P1634 (Flash Code 55)
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 boost pressure sensor
harness connector.

Connect a DMM between the 5 volts reference
circuit of the boost pressure sensor harness
(pin 3 of J-216 connector) and a known good
ground.

Turn ON the ignition, with engine OFF.

Is the DMM voltage less than the specified value?

5.5 volts

Go to Step 4

Go to Step 5

Is the DMM voltage more than the specified value
at Step 3?

4.5 volts

Go to Step 7

Go to Step 6

Engine Control System (4HK1) 6E-267

Test the 5 volts reference circuit 3 between the
engine control module (ECM) (pin 95 of E-111
connector) and the boost pressure sensor (pin
3 of J-216 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 9

Go to Step 8

Test the 5 volts reference circuit 3 between the
ECM (pin 95 of E-111 connector) and the
boost pressure sensor (pin 3 of J-216
connector) for a short to ground or short to the
low reference circuit.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 8

Replace the boost pressure sensor. Refer to Boost
Pressure Sensor Replacement in this section.

Did you complete the replacement?

—

Go to Step 9

Go to Step 8

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 9

Go to Step 8

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine.

Operate the vehicle within the Conditions for
Running the DTC.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 10

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-268 Engine Control System (4HK1)

P1635 (Flash Code 55)

Circuit Description
The engine control module (ECM) provides 5 volts
reference voltage through the reference circuit 5 to the
following sensors:

• Fuel rail pressure (FRP) sensor
• EGR valve position sensor

The ECM also provides 5 volts reference voltage
through the reference circuit 2 to the following sensors:

• Accelerator pedal position (APP) sensor 2
• Barometric pressure (BARO) sensor

The 5 volts reference circuits 2 and 5 are independent
of each other outside of the ECM, but are bussed
together inside the ECM. Therefore, a short circuit
condition on one sensor 5 volts reference circuit may
affect the entire 5 volt reference circuit 2 and 5. The
ECM monitors the voltage on the 5 volts reference
circuit 2 and 5. If the ECM detects the voltage is
excessively low or high, this DTC and DTC P1632 will
also set.

Condition for Running the DTC

• DTC P1630 is not set.
• The ignition switch is ON.
• The battery voltage is between 16 – 32 volts.

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

• The ECM detects that the 5 volts reference circuit

2 or 5 voltage is less than 4.5 volts.

• The ECM detects that the 5 volts reference circuit

2 or 5 voltage is more than 5.5 volts.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM blinks the exhaust brake indicator lamp

when the diagnostic runs and fails.

• The ECM limits accelerator control range.
• The ECM inhibits pilot injection.
• The ECM inhibits EGR valve control.
• The ECM inhibits exhaust brake control.

Condition for Clearing the MIL / DTC

• The ECM turns OFF the MIL and exhaust brake

indicator lamp 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 P1635 (Flash Code 55)
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 DTC P1632

Go to Diagnostic

Aids

Engine Control System (4HK1) 6E-269

P1681 (Flash Code 46)

Circuit Description
The engine control module (ECM) controls the exhaust
brake which energizes the intake throttle solenoid valve
and exhaust brake solenoid valve based on vehicle
running condition. The ECM commands each solenoid
valve to close each throttle valve by applying vacuum.
If the ECM detects that an open circuit or short to
ground on the exhaust brake solenoid valve control
circuit, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.
• The battery voltage is between 16 – 32 volts.
• The engine is running.

Condition for Setting the DTC

• The ECM detects a low voltage condition on the

exhaust brake solenoid valve control circuit for
longer than 10 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 blinks the exhaust brake indicator lamp

when the diagnostic runs and fails.

• The ECM inhibits exhaust brake control.

Condition for Clearing the MIL / DTC

• The ECM turns OFF the MIL when the key is

cycled after a current DTC clears.

• The ECM turns OFF the exhaust brake indicator

lamp when the diagnostic runs and does not fail.

• 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 P1681 (Flash Code 46)
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.

Turn ON the ignition, with the engine OFF.

Perform the Exhaust Brake Control test with
the Tech 2.

Command the Exhaust Brake ON with the
Tech 2.

Does the exhaust brake solenoid valve click when
commanded ON with the Tech 2 (note that intake
throttle solenoid valve also click when commanded
ON)?

—

Go to Step 3

Go to Step 4

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 13

Go to Diagnostic

Aids

Turn OFF the ignition.

Disconnect the exhaust brake solenoid valve
harness connector.

Connect a test lamp between the voltage feed
circuit of the exhaust brake solenoid valve
harness (pin 1 of J-31 connector) and a known
good ground.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 5

Go to Step 7

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