Isuzu N-Series. Manual - part 704

6E-238    Engine Control System (4HK1) 

P1271 (Flash Code 24)

Circuit Description
The accelerator pedal position (APP) sensor is
mounted on the accelerator pedal control assembly.
The sensor is made up of two individual sensors within
one housing. The APP sensor 1 and APP sensor 2 are
potentiometer type sensors, each with the following
circuits.

• 5 volts reference circuit
• Low reference circuit
• Signal circuit

The engine control module (ECM) supplies 5 volts to
the APP sensor on the 5 volts reference circuits. The
ECM also provides a ground on the low reference
circuits. The APP sensor provides a signal to the ECM
on the APP sensor signal circuits, which is relative to
the position changes of the accelerator pedal angle.
The APP sensor 1 signal voltage is low at rest and
increases as the pedal is depressed. The APP sensor 2
signal voltage is high at rest and decreases as the
pedal is depressed. If the ECM detects that the APP
sensor 1 signal and the APP sensor 2 signal are out of
the correlation, this DTC will set.

Condition for Running the DTC

• DTCs P1630, P1631 and P1632 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 APP sensor 1 and

sensor 2 are more than 45% out of range of each
other.

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 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 at next driving cycle.

• 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 P1271 (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

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 P1277, P1278, P1282, P1283, P1631 or
P1632 set?

—

Go to Applicable 

DTC

Go to Step 3

3

1.

Turn OFF the ignition for 30 seconds.

2.

Start the engine.

3.

Monitor the DTC Information with the Tech 2.

4.

Fully depress and release the accelerator
pedal.

Does the DTC fail this ignition?

—

Go to Step 4

Go to Diagnostic 

Aids

 Engine Control System (4HK1)    6E-239

4

1.

Turn OFF the ignition.

2.

Disconnect the accelerator pedal position
(APP) sensor harness connector.

3.

Inspect for an intermittent, for poor
connections and corrosion at the harness
connector of the APP sensor (pins 1, 2, 3, 4, 5
and 6 of B-280 connector).

4.

Disconnect the engine control module (ECM)
harness connector.

5.

Inspect for an intermittent, for poor
connections and corrosion on each APP
sensor circuit at the harness connector of the
ECM (pins 41, 42, 60, 61, 63 and 64 of J-191
connector).

6.

Test for high resistance on each APP sensor
circuit.

7.

Repair the connection(s) or circuit(s) as
necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 5

5

1.

Test the APP sensor 1 and sensor 2 signal
circuit between the ECM (pin 63 and 64 of J-
191 connector) and the APP sensor (pin 2 and
5 of B-280 connector) for a short circuit each
other.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 6

6

Replace the APP sensor. Refer to Accelerator
Pedal Position (APP) Sensor Replacement in this
section. (APP sensor 1 and sensor 2 is internal to
APP sensor assembly)

Did you complete the replacement?

—

Go to Step 7

—

7

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.

Fully depress and release the accelerator
pedal.

Does the DTC fail this ignition?

—

Go to Step 8

Go to Step 10

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

—

9

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.

Fully depress and release the accelerator
pedal.

Does the DTC fail this ignition?

—

Go to Step 2

Go to Step 10

Step

Action

Value(s)

Yes

No

6E-240    Engine Control System (4HK1) 

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

No

 Engine Control System (4HK1)    6E-241

P1277 (Flash Code 24)

Circuit Description
The accelerator pedal position (APP) sensor is
mounted on the accelerator pedal control assembly.
The sensor is made up of two individual sensors within
one housing. The engine control module (ECM) uses
the APP sensors to determine the amount of
acceleration or deceleration desired by the person
driving the vehicle via the fuel injector control. The APP
sensor 1 has the following circuits.

• 5 volts reference circuit
• Low reference circuit
• APP sensor 1 signal circuit

The ECM supplies 5 volts to the APP sensor 1 on the 5
volts reference circuit. The ECM also provides a ground
on the low reference circuit. The APP sensor 1
provides a signal to the ECM on the APP sensor 1
signal circuit, which is relative to the position changes
of the accelerator pedal angle. The ECM monitors the
APP sensor 1 signal for voltages outside the normal
range of the APP sensor 1. If the ECM detects an
excessively low APP sensor 1 signal 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

• The ECM detects that the APP sensor 1 signal

voltage is less than 0.2 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 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 at next driving cycle.

• 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.

• APP sensor 1 may have an intermittent open

somewhere in the pedal range.

DTC P1277 (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

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 P1631 also set?

—

Go to DTC P1631

Go to Step 3

3

1.

Turn ON the ignition, with the engine OFF.

2.

Observe the Accelerator Pedal Position (APP)
Sensor 1 parameter with the Tech 2.

Is the APP Sensor 1 parameter less than the
specified value?

0.2 volts

Go to Step 4

Go to Diagnostic 

Aids