Isuzu N-Series. Service manual — part 751

Engine Control System (4JH1) 6E-55

P1120

(1)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit High
Voltage

• The ignition switch

is ON.

• The ECM detects

that the APP
sensor signal
voltage is more
than 4.9 volts for
0.5 seconds.

• Sensor 5V reference

circuit is short to battery
or ignition voltage.

• Sensor 5V reference

circuit is short to ground
or short to the low
reference circuit.

• Sensor signal circuit is

short to any 5V
reference circuit, short to
battery or ignition voltage
circuit.

• Sensor low reference

circuit is open circuit or
high resistance.

• Poor harness connector

connection.

• Faulty APP sensor.
• Faulty ECM.

P1120

(2)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit Low
Voltage

• The ignition switch

is ON.

• The ECM detects

that the APP
sensor signal
voltage is less than
0.3 volts for 0.5
seconds.

• Sensor 5V reference

circuit is open circuit,
high resistance, short to
ground or short to the
low reference circuit.

• Sensor signal circuit is

open circuit, high
resistance, short to
ground or short to the
low reference circuit.

• Poor harness connector

connection.

• Faulty APP sensor.
• Faulty ECM.

P1120

(7)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit 5V
Reference High
Voltage

• The ignition switch

is ON.

• The ECM detects

that the APP
sensor voltage
supply circuit is
more than 5.2 volts
for 0.5 seconds.

• Sensor 5V reference

circuit is short to battery
or ignition voltage circuit.

• Faulty ECM.

P1120

(9)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit 5V
Reference Low
Voltage

• The ignition switch

is ON.

• The ECM detects

that the APP
sensor voltage
supply circuit is
less than 4.6 volts
for 0.5 seconds.

• Sensor 5V reference

circuit is short to ground
or short to the low
reference circuit.

• Faulty APP sensor.
• Faulty ECM.

DTC

(Symptom

Code)

Flash
Code

MIL

Status

DTC Name on

Tech 2

Condition for Running

the DTC

Condition for Setting

the DTC

Possible Cause

6E-56 Engine Control System (4JH1)

P1120

(D)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit
Correlation

• The ignition switch

is ON.

• The engine speed

is higher than 1700
RPM.

• The vehicle speed

is higher than 1.5
km/h (1MPH).

• The ECM detects

APP sensor angle
is stationary more
than 18%, then
brake pedal is
depressed for
longer than 2
seconds.

• Brake pedal 1 switch

signal circuit is open
circuit, high resistance,
short to battery or
ignition voltage.

• Accelerator pedal stuck.
• Intake throttle valve

stuck.

• Intake throttle valve

control cable damaged,
stuck or no free play.

• Misadjusted APP sensor.
• Faulty APP sensor.
• Misadjusted brake pedal

switch.

• Faulty brake pedal

switch.

• Faulty ECM.

P1120

(E)

21

ON

Accelerator
Pedal Position
(APP) Sensor
Circuit
Correlation

• The ignition switch

is ON.

• The ECM detects

APP sensor angle
is more than 18%,
then idle switch is
ON for longer than
0.6 seconds.

• APP sensor low

reference circuit is high
resistance.

• Idle switch signal circuit

is short to ground.

• Poor harness connector

connection.

• Faulty APP sensor.
• Faulty idle switch.
• Faulty ECM.

P1173

(3)

22

OFF

Limitation of
Injection
Quantity

• The ignition switch

is ON.

• The ECM detects

an excessive high
coolant
temperature for
longer than 30
seconds.

• Engine overheat.
• Faulty engine cooling

system.

• Faulty ECT sensor.

P1173

(7)

22

OFF

Limitation of
Injection
Quantity

• The ignition switch

is ON.

• The ECM detects

an excessive high
FT for longer than
30 seconds.

• Faulty PCU.

P1173

(A)

22

OFF

Limitation of
Injection
Quantity

• The ignition switch

is ON.

• The ECM detects

an excessive low
FT for longer than
30 seconds.

• Faulty PCU.

P1335

(A)

43

ON

Crankshaft
Position (CKP)
Sensor Circuit

• The ignition switch

is ON.

• The PCU detects

CKP sensor signal
from the ECM is
faulty.

• CKP sensor signal

output circuit is open
circuit, high resistance,
short to ground, short to
battery or ignition
voltage.

• Poor harness connector

connection.

• Faulty PCU.
• Faulty ECM.

DTC

(Symptom

Code)

Flash
Code

MIL

Status

DTC Name on

Tech 2

Condition for Running

the DTC

Condition for Setting

the DTC

Possible Cause

Engine Control System (4JH1) 6E-57

P1345

(A)

41

ON

Crankshaft
Position (CKP)
– Camshaft
Position (CMP)
Correlation

—

• The PCU received

faulty fuel injection
pump CMP sensor
signal for 1
second.

• Faulty fuel injection

pump.

• Faulty PCU.

P1520

(A)

47

ON

Park/Neutral
Position Switch
Circuit

• The ignition switch

is ON.

• The engine speed

is higher than 1500
RPM.

• The vehicle speed

is higher than 64
km/h (40MPH).

• The clutch pedal is

released.

• The ECM detects

that the neutral
switch signal is
continuously ON
(neutral) during
three consecutive
driving cycles.

• Neutral switch signal

circuit is short to battery
or ignition voltage.

• Faulty neutral switch.
• Faulty ECM.

P1520

(B)

47

ON

Park/Neutral
Position Switch
Circuit

• The ignition switch

is ON.

• The engine speed

is higher than 665
RPM.

• The vehicle speed

is lower than 2 km/
h (3MPH).

• The clutch pedal is

released after once
depressed.

• The ECM detects

that the neutral
switch signal is
continuously OFF
(other than neutral)
during three
consecutive driving
cycles.

• Neutral switch ignition

voltage feed circuit is
open circuit or high
resistance.

• Neutral switch signal

circuit is open circuit or
high resistance.

• Poor harness connector

connection.

• Faulty neutral switch.
• Faulty ECM.

P1576

(4)

71

ON

Exhaust Brake
Solenoid Circuit
Low Voltage

• The ignition switch

is ON.

• The ECM detects

that the low voltage
condition on the
exhaust brake
solenoid valve
control circuit for
longer than 3
seconds when the
solenoid valve is
commanded OFF.

• Exhaust brake solenoid

valve ignition voltage
feed circuit is open
circuit or high resistance.

• Exhaust brake solenoid

valve control circuit is
open circuit, high
resistance or short to
ground.

• Poor harness connector

connection.

• Faulty exhaust brake

solenoid valve.

• Faulty ECM.

P1576

(8)

71

ON

Exhaust Brake
Solenoid Circuit
High Voltage

• The ignition switch

is ON.

• The ECM detects

that the high
voltage condition
on the exhaust
brake solenoid
valve control circuit
for longer than 3
seconds when the
solenoid valve is
commanded ON.

• Exhaust brake solenoid

valve control circuit is
short to battery or
ignition voltage circuit.

• Faulty exhaust brake

solenoid valve.

• Faulty ECM.

P1605

(C)

55

ON

Control Module
Internal
Performance

—

• The ECM detects

internal seed or
key file in
EEPROM data is
destroyed.

• Faulty ECM.

DTC

(Symptom

Code)

Flash
Code

MIL

Status

DTC Name on

Tech 2

Condition for Running

the DTC

Condition for Setting

the DTC

Possible Cause

6E-58 Engine Control System (4JH1)

P1605

(D)

55

ON

Control Module
Internal
Performance

—

• The ECM detects

reading or writing
from the EEPROM
data is failed
during initialization.

• Faulty ECM.

P1605

(E)

55

ON

Control Module
Internal
Performance

—

• The ECM detects

total sum of
EEPROM data is
not equal to
registered value
during initialization.

• Faulty ECM.

P1625

(A)

76

OFF

ECM Main
Relay Circuit

—

• The ECM detects

that the ECM main
relay is turned OFF
before
commanded
turned OFF.

• ECM main relay control

circuit is intermittently
open circuit or high
resistance.

• ECM battery voltage

feed circuit is
intermittently open or
high resistance.

• Faulty ECM main relay.

P1625

(B)

76

OFF

ECM Main
Relay Circuit

• The ignition switch

is OFF.

• The ECM detects

that the ECM main
relay is turned ON
for longer than 2
seconds.

• ECM main relay control

circuit is short to ground.

• ECM battery voltage

circuit is short to battery.

• Faulty ECM main relay.
• Faulty ECM.

P1630

(A)

51

ON

Injection Pump
Fuel Metering
Control

—

• The ECM detects

that the PCU
monitored fuel
injection solenoid
valve control
current is too high.

• Faulty fuel injection

pump.

• Faulty PCU.

P1630

(B)

51

ON

Injection Pump
Fuel Metering
Control

—

• The ECM detects

that the PCU
continuously flow
the control current
to the fuel injection
solenoid valve.

• Faulty fuel injection

pump.

• Faulty PCU.

P1650

(A)

44

ON

CAN Device
Offline

—

• The ECM detects

that the PCU
receives from the
CAN controller
reset or Bus
Offline.

• CAN high circuit is open

circuit, high resistance,
short to ground, short to
battery or ignition
voltage.

• CAN low circuit is open

circuit, high resistance,
short to ground, short to
battery or ignition
voltage.

• Electrical interference.
• Magnetic interference.
• Faulty PCU.
• Faulty ECM.

DTC

(Symptom

Code)

Flash
Code

MIL

Status

DTC Name on

Tech 2

Condition for Running

the DTC

Condition for Setting

the DTC

Possible Cause