Isuzu N-Series. Manual - part 683

6E-154    Engine Control System (4HK1) 

P0237 (Flash Code 32)

Circuit Description
The boost pressure sensor is located in the air
induction tubing. The boost pressure sensor is a
transducer that varies voltage according to changes in
the air pressure inside the air tubing. The boost
pressure sensor has the following circuits.

• 5 volts reference circuit
• Low reference circuit
• Boost pressure sensor signal circuit

The engine control module (ECM) supplies 5 volts to
the boost pressure sensor on the 5 volts reference
circuit. The ECM also provides a ground on the low
reference circuit. The boost pressure sensor provides a
signal to the ECM on the boost pressure signal circuit
which is relative to the pressure changes in the
manifold. The ECM should detect a low signal voltage
at a low boost pressure, such as low engine load. The
ECM should detect high signal voltage at a high boost
pressure, such as high engine load. The ECM monitors
the boost pressure sensor signal for voltage outside the
normal range of the boost pressure sensor. If the ECM
detects an excessively low boost pressure sensor
signal voltage, this DTC will set.

Condition for Running the DTC

• DTCs P1630 and P1634 are not set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.

Condition for Setting the DTC

• The ECM detects that the boost pressure sensor

signal voltage is less than 0.1 volts for 5 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM uses a boost pressure substitution of

100 kPa (14.5 psi) for engine control.

• 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 P0237 (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 Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

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

Is DTC P1634 also set?

—

Go to DTC P1634

Go to Step 3

3

1.

Start the engine.

2.

Observe the Boost Pressure Sensor
parameter with the Tech 2.

Is the Boost Pressure Sensor parameter less than
the specified value?

0.1 volts

Go to Step 4

Go to Diagnostic 

Aids

 Engine Control System (4HK1)    6E-155

4

1.

Turn OFF the ignition.

2.

Disconnect the boost pressure sensor
harness connector.

3.

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.

4.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage more than the specified value?

4.5 volts

Go to Step 5

Go to Step 6

5

1.

Turn OFF the ignition.

2.

Connect a 3-amp fused jumper wire between
the 5 volts reference circuit and the signal
circuit of the boost pressure sensor harness
(pins 3 and 2 of J-216 connector).

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the Boost Pressure Sensor
parameter with the Tech 2.

Is the Boost Pressure Sensor parameter more than
specified value?

4.5 volts

Go to Step 8

Go to Step 7

6

1.

Test the 5 volts reference circuit between the
engine control module (ECM) (pin 95 of E-111
connector) and the boost pressure sensor (pin
3 of J-216 connector) for an open circuit or
high resistance.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 9

7

1.

Test the signal circuit between the ECM (pin
91 of E-111 connector) and the boost pressure
sensor (pin 2 of J-216 connector) for the
following conditions:

• An open circuit
• A short to ground
• A short to the low reference circuit
• High resistance

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 9

8

1.

Turn OFF the ignition.

2.

Inspect for an intermittent and for poor
connections at the harness connector of the
boost pressure sensor (pins 2 and 3 of J-216
connector).

3.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 10

9

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for poor
connections on the boost pressure sensor
circuits at the harness connector of the ECM
(pins 91 and 95 of E-111 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 11

Step

Action

Value(s)

Yes

No

6E-156    Engine Control System (4HK1) 

10

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

Did you complete the replacement?

—

Go to Step 12

—

11

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 12

—

12

1.

Reconnect all previously disconnected
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine.

5.

Operate the vehicle within the Conditions for
Running the DTC.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 13

13

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

No

 Engine Control System (4HK1)    6E-157

P0238 (Flash Code 32)

Circuit Description
The boost pressure sensor is located in the air
induction tubing. The boost pressure sensor is a
transducer that varies voltage according to changes in
the air pressure inside the air tubing. The boost
pressure sensor has the following circuits.

• 5 volts reference circuit
• Low reference circuit
• Boost pressure sensor signal circuit

The engine control module (ECM) supplies 5 volts to
the boost pressure sensor on the 5 volts reference
circuit. The ECM also provides a ground on the low
reference circuit. The boost pressure sensor provides a
signal to the ECM on the boost pressure signal circuit
which is relative to the pressure changes in the
manifold. The ECM should detect a low signal voltage
at a low boost pressure, such as low engine load. The
ECM should detect high signal voltage at a high boost
pressure, such as high engine load. The ECM monitors
the boost pressure sensor signal for voltage outside the
normal range of the boost pressure sensor. If the ECM
detects an excessively high boost pressure sensor
signal voltage, this DTC will set.

Condition for Running the DTC

• DTCs P1630 and P1634 are not set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.

Condition for Setting the DTC

• The ECM detects that the boost pressure sensor

signal voltage is more than 4.9 volts for 5 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM uses a boost pressure substitution of

100 kPa (14.5 psi) for engine control.

• 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 P0238 (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 Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Observe the Boost Pressure Sensor
parameter with the Tech 2.

Is the Boost Pressure Sensor parameter more than
the specified value?

4.9 volts

Go to Step 3

Go to Diagnostic 

Aids

3

1.

Start the engine.

2.

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

Is DTC P1634 also set?

—

Go to Step 4

Go to Step 5

4

1.

Turn OFF the ignition.

2.

Disconnect the boost pressure sensor
harness connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the Boost Pressure Sensor
parameter with the Tech 2.

Is the Boost Pressure Sensor parameter less than
the specified value?

0.1 volts

Go to DTC P1634

Go to Step 7