Isuzu N-Series. Manual - part 701

6E-226    Engine Control System (4HK1) 

5

1.

Turn OFF the ignition.

2.

Disconnect the PTO throttle sensor harness
connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the PTO Remote Throttle Sensor
parameter with the Tech 2.

Is the PTO Remote Throttle Sensor parameter less
than the specified value?

0.2 volts

Go to Step 6

Go to Step 7

6

1.

Turn OFF the ignition.

2.

Connect a test lamp between the low
reference circuit of the PTO throttle sensor
harness (pin 3 of J-166 connector) and battery
voltage.

3.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 9

Go to Step 8

7

Important:
The PTO throttle 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 70 of J-191
connector) and the PTO throttle sensor (pin 2
of J-166 connector) for the following
conditions:

• A short to battery or ignition voltage
• A short to any 5 volts reference

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

8

1.

Test the low reference circuit between the
ECM (pin 41 of J-191 connector) and the PTO
throttle sensor (pin 3 of J-166 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 13

Go to Step 10

9

1.

Turn OFF the ignition.

2.

Inspect for an intermittent and for a poor
connection at the harness connector of the
PTO throttle sensor (pin 3 of J-166 connector).

3.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

10

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for a poor
connection on the PTO throttle sensor circuit
at the harness connector of the ECM (pin 41
of J-191 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

11

Replace the PTO throttle sensor.

Did you complete the replacement?

—

Go to Step 13

—

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-227

12

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 13

—

13

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.

Observe the PTO Remote Throttle Sensor
parameter with the Tech 2 while turning the
PTO throttle sensor.

Is the PTO Remote Throttle Sensor parameter
more than the specified value?

4.8 volts

Go to Step 3

Go to Step 14

14

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-228    Engine Control System (4HK1) 

P1225 (Flash Code 31)

Circuit Description
The idle up sensor controls the idle speed during warm-
up and it is installed in the driver’s side instrument
panel. This sensor is active only when the gear position
is in the neutral position. When the selector lever is
moved to another position, the signal is ignored. The
engine control module (ECM) receives the idle up
signal from the idle up sensor and controls the fuel
injection quantity. The idle up sensor has following
circuits.

• 5 volts reference circuit
• Low reference circuit
• Idle up sensor signal circuit

The ECM monitors the idle up sensor signals for
voltages outside the normal range of the idle up sensor.
If the ECM detects an excessively low or high idle up
sensor voltage, this DTC will set.

Condition for Running the DTC

• DTCs P1630 and P1631 are not set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.

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

• The ECM detects that the idle up sensor signal

voltage is less than 0.1 volts for 5 second.

• The ECM detects that the idle up sensor signal

voltage is more than 4.9 volts for 5 second.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM disables idle up sensor 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.

• Idle up sensor may have an intermittent open

somewhere in the operating range.

DTC P1225 (Flash Code 31)
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.

Fully turn the idle up sensor to lowest position
(full counterclockwise direction) and highest
position (full clock wise direction) while
observing the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter within the
specified valve?

0.2 – 4.8 volts

Go to Diagnostic 

Aids

Go to Step 3

3

1.

Start the engine.

2.

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

Is DTC P1631 also set?

—

Go to Step 4

Go to Step 5

4

Is the Idle Up Sensor parameter less than the
specified value at Step 2?

0.1 volts

Go to DTC P1631

Go to Step 8

 Engine Control System (4HK1)    6E-229

5

1.

Turn ON the ignition, with the engine OFF.

2.

Turn the idle up sensor to lowest position (full
counterclockwise direction).

3.

Observe the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter less than the
specified value?

0.1 volts

Go to Step 6

Go to Step 9

6

1.

Turn OFF the ignition.

2.

Disconnect the idle up sensor harness
connector.

3.

Connect a DMM between the 5 volts reference
circuit of the idle up sensor harness (pin 3 of
B-281 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 7

Go to Step 11

7

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 idle up sensor harness (pin 2 and
3 of B-281 connector).

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter more than the
specified value?

4.5 volts

Go to Step 15

Go to Step 12

8

1.

Turn OFF the ignition.

2.

Disconnect the idle up sensor harness
connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter less than the
specified value?

0.1 volts

Go to DTC P0631

Go to Step 13

9

1.

Turn OFF the ignition.

2.

Disconnect the idle up sensor harness
connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Observe the Idle Up Sensor parameter with
the Tech 2.

Is the Idle Up Sensor parameter less than the
specified value?

0.1 volts

Go to Step 10

Go to Step 13

10

1.

Turn OFF the ignition.

2.

Connect a test lamp between the low
reference circuit of the idle up sensor harness
(pin 1 of B-281 connector) and battery voltage.

3.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 15

Go to Step 14

Step

Action

Value(s)

Yes

No