Isuzu N-Series. Manual - part 755

 Engine Control System (4JH1)    6E-71

P0110 (Symptom Code 1) (Flash Code 23)

Circuit Description
The intake air temperature (IAT) sensor is fitted
between the air cleaner and turbocharger internal to
the mass air flow (MAF) sensor.  The IAT sensor is a
variable resistor.  The IAT sensor has a signal circuit
and a low reference circuit.  The IAT sensor measures
the temperature of the air entering the engine.  The
engine control module (ECM) supplies 5 volts to the
IAT signal circuit and a ground for the IAT low reference
circuit.  When the IAT sensor is cold, the sensor
resistance is high.  When the air temperature
increases, the sensor resistance decreases.  With high
sensor resistance, the ECM detects a high voltage on
the IAT signal circuit.  With lower sensor resistance, the
ECM detects a lower voltage on the IAT signal circuit.  If
the ECM detects an excessively high IAT signal
voltage, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.

Condition for Setting the DTC

• The ECM detects that the IAT sensor signal

voltage is more than 4.7 volts for 3 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM uses an IAT substitution of 0

°C (32°F)

for engine control.

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.

• Use the Temperature vs.  Resistance table to test

the IAT sensor at various temperature levels to
evaluate the possibility of a skewed sensor.  A
skewed sensor could result in poor driveability
concerns.

Notice:

• The mass air flow (MAF) sensor is heated and as a

result the IAT sensor may indicate a higher than
normal intake temperature if the ignition switch is
being ON.

DTC P0110 (Symptom Code 1) (Flash Code 23)
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 ON the ignition, with the engine OFF.

3.

Observe the Intake Air Temperature (IAT)
parameter with the Tech 2.

Is the IAT parameter less than the specified value?

-38

°C (-36°F)

Go to Step 3

Go to Diagnostic 

Aids

3

1.

Turn OFF the ignition.

2.

Disconnect the mass air flow/intake air
temperature (MAF/IAT) sensor harness
connector.

3.

Connect a DMM between the signal circuit of
the IAT sensor harness (pin 1 of J-182
connector) and a known good ground.

4.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage more than the specified value?

5.3 volts

Go to Step 4

Go to Step 5

6E-72    Engine Control System (4JH1) 

4

Important:
The IAT sensor may be damaged if the sensor
signal circuit is shorted to a voltage source.

1.

Test the signal circuit between the engine
control module (ECM) (pin 84 of B-233
connector) and the IAT sensor (pin 1 of J-182
connector) for a short to battery or ignition
voltage.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 13

5

1.

Turn OFF the ignition.

2.

Connect a 3-amp fused jumper wire between
the signal circuit and the low reference circuit
of the IAT sensor harness (pins 1 and 3 of J-
182 connector).

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the IAT parameter with the Tech 2.

Is the IAT parameter more than the specified
value?

110

°C (230°F)

Go to Step 9

Go to Step 6

6

1.

Turn OFF the ignition.

2.

Connect a 3-amp fused jumper wire between
the signal circuit of the IAT sensor harness
(pin 1 of J-182 connector) and a known good
ground.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the IAT parameter with the Tech 2.

Is the IAT parameter more than the specified
value?

110

°C (230°F)

Go to Step 8

Go to Step 7

7

1.

Test the signal circuit between the ECM (pin
84 of B-233 connector) and the IAT sensor
(pin 1 of J-182 connector) for an open circuit
high resistance.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 11

8

1.

Test the low reference circuit between the
ECM (pin 92 of B-233 connector) and the IAT
sensor (pin 3 of J-182 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 14

Go to Step 11

9

1.

Test the signal circuit between the ECM (pin
84 of B-233 connector) and the IAT sensor
(pin 1 of J-182 connector) for a short to any 5
volts reference circuit.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 10

10

1.

Turn OFF the ignition.

2.

Inspect for an intermittent and for poor
connections at the harness connector of the
IAT sensor (pins 1 and 3 of J-182 connector).

3.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 12

Step

Action

Value(s)

Yes

No

 Engine Control System (4JH1)    6E-73

11

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for poor
connections on the IAT sensor circuits at the
harness connector of the ECM (pins 84 and
92 of B-233 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 13

12

Replace the IAT sensor.  Refer to Mass Air Flow
Sensor Replacement in this section.  (IAT sensor is
internal to MAF sensor)

Did you complete the replacement?

—

Go to Step 14

—

13

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 14

—

14

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.

Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 2

Go to Step 15

15

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

6E-74    Engine Control System (4JH1) 

P0110 (Symptom Code 2) (Flash Code 23)

Circuit Description
The intake air temperature (IAT) sensor is fitted
between the air cleaner and turbocharger internal to
the mass air flow (MAF) sensor.  The IAT sensor is a
variable resistor.  The IAT sensor has a signal circuit
and a low reference circuit.  The IAT sensor measures
the temperature of the air entering the engine.  The
engine control module (ECM) supplies 5 volts to the
IAT signal circuit and a ground for the IAT low reference
circuit.  When the IAT sensor is cold, the sensor
resistance is high.  When the air temperature
increases, the sensor resistance decreases.  With high
sensor resistance, the ECM detects a high voltage on
the IAT signal circuit.  With lower sensor resistance, the
ECM detects a lower voltage on the IAT signal circuit.  If
the ECM detects an excessively low IAT signal voltage,
this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.

Condition for Setting the DTC

• The ECM detects that the IAT sensor signal

voltage is less than 0.3 volts for 3 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM uses an IAT substitution of 0

°C (32°F)

for engine control.

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.

• Use the Temperature vs.  Resistance table to test

the IAT sensor at various temperature levels to
evaluate the possibility of a skewed sensor.  A
skewed sensor could result in poor driveability
concerns.

Notice:

• The mass air flow (MAF) sensor is heated and as a

result the IAT sensor may indicate a higher than
normal intake temperature if the ignition switch is
being ON.

DTC P0110 (Symptom Code 2) (Flash Code 23)
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 ON the ignition, with the engine OFF.

3.

Observe the Intake Air Temperature (IAT)
parameter with the Tech 2.

Is the IAT parameter more than the specified
value?

110

°C (230°F)

Go to Step 3

Go to Diagnostic 

Aids

3

1.

Turn OFF the ignition.

2.

Disconnect the mass air flow/intake air
temperature (MAF/IAT) sensor harness
connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the IAT parameter with the Tech 2.

Is the IAT parameter less than the specified value?

-38

°C (-36°F)

Go to Step 5

Go to Step 4