Isuzu N-Series. Manual - part 781

Engine Control System (4JH1) 6E-175

Test the 5 volts reference circuit between the
engine control module (ECM) (pin 57 of B-234
connector) and the APP sensor (pin 3 of B-80
connector) for the following conditions:

• A short to ground
• A short to the low reference circuit

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

Replace the accelerator pedal position sensor.
Refer to Accelerator Pedal Position Sensor
Replacement in this section.

Did you complete the replacement?

—

Go to Step 7

—

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 7

—

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Turn ON the ignition, with the engine OFF.

Fully depress and release the accelerator
pedal many times.

Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 8

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

6E-176 Engine Control System (4JH1)

P1120 (Symptom Code D) (Flash Code 21)

Circuit Description
The accelerator pedal position (APP) sensor is
mounted on the accelerator pedal bracket. 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
injection control. The APP sensor has the following
circuits.

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

The ECM supplies 5 volts to the APP sensor on the 5
volts reference circuit. The ECM also provides a
ground on the low reference circuit. The APP sensor
provides a signal to the ECM on the APP sensor signal
circuit, which is relative to the position changes of the
accelerator pedal angle.
The brake pedal switch is installed on the brake pedal
bracket. The brake pedal 1 switch is a normally open
type switch and the brake pedal 2 switch is a normally
closed type switch. When the brake pedal is pressed,
the brake pedal 1 switch signal is provided to the ECM
and the stoplights are turned ON. Then, the brake
pedal 2 switch signal to the ECM is stopped (low
voltage).
If the ECM detects accelerator pedal or APP sensor
signal is stuck while brake pedal is depressed, this
DTC will set.

Condition for Running the DTC

• The ignition switch is ON.
• The engine speed is higher than 1700 RPM.
• The vehicle speed is higher than 1.5 km/h (1

MPH).

Condition for Setting the DTC

• The ECM detects APP sensor angle is stationary

more than 18%, then brake pedal is depressed for
longer than 2 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 engine speed substitution of

1400 RPM.

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.

• Misadjusted brake pedal switch may set this DTC.
• Misadjusted APP sensor may set this DTC.
• A sticking or intermittently sticking the pedal may

set this DTC.

DTC P1120 (Symptom Code D) (Flash Code 21)
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

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic

System Check –

Engine Controls

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Turn ON the ignition, with the engine OFF.

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

Was DTC P0703 (Symptom Code A or B) or P1120
(Symptom Code 1, 7, 9 or E) set?

—

Go to Applicable

DTC

Go to Step 3

Turn ON the ignition, with the engine OFF.

Observe the Brake Pedal 1 Switch parameter
with the Tech 2 while fully depressing and
releasing the brake pedal.

Does the Tech 2 indicate Applied when the brake
pedal is applied and Released when the brake
pedal is released?

—

Go to Step 9

Go to Step 4

Engine Control System (4JH1) 6E-177

Check to ensure the brake pedal switch is
adjusted correctly. The plunger should be all
the way in when the pedal is released, yet
should not impede with the brake pedal full
upward travel.

Adjust the brake pedal switch as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 5

Turn OFF the ignition.

Disconnect the brake pedal switch harness
connector.

Turn ON the ignition, with the engine OFF.

Observe the Brake Pedal 1 Switch parameter
with the Tech 2 while momentarily jumping 3-
amp fused jumper wire across the brake pedal
1 switch harness connector between pins 1
and 4 of the B-66 connector.

Does the Tech 2 indicate Applied when the circuit is
jumpered and Released when the circuit is not
jumpered?

—

Go to Step 8

Go to Step 6

Test the brake pedal 1 switch signal circuit
between the ECM (pin 30 of B-234 connector)
and the brake pedal 1 switch (pin 4 of B-66
connector) for the following conditions:

• An open circuit
• A short to battery or ignition voltage
• High resistance.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 7

Turn OFF the ignition.

Disconnect the ECM harness connector.

Inspect for an intermittent and for a poor
connection on the brake switch circuit at the
harness connector of the ECM (pin 30 of B-
234 connector).

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

Replace the brake pedal switch. Refer to Brake
Pedal Switch Replacement in this section.

Did you complete the replacement?

—

Go to Step 13

—

Turn ON the ignition, with the engine OFF.

Fully depress and release the accelerator
pedal many times while observing the
Accelerator Pedal Position (APP) parameter
with the Tech 2.

Is the APP parameter smoothly changed within 0 to
100% when the accelerator pedal is depressed and
released?

—

Go to Diagnostic

Aids

Go to Step 10

Step

Action

Value(s)

Yes

6E-178 Engine Control System (4JH1)

Turn OFF the ignition.

Inspect for the following conditions:

• APP sensor is misadjusted.
• An accelerator pedal that is stuck

depressed.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

Replace the accelerator pedal position sensor.
Refer to Accelerator Pedal Position Sensor
Replacement in this section.

Did you complete the replacement?

—

Go to Step 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 13

—

Reconnect all previously disconnected
harness connector(s).

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Turn ON the ignition, with the engine OFF.

Observe the APP parameter while fully
depressing and releasing the accelerator
pedal many times.

Also observe the Brake Pedal 1 Switch
parameter with the Tech 2 while depressing
and releasing the brake pedal.

Does the Tech 2 indicate the APP parameter
smoothly changed within 0 to 100% when the
accelerator pedal is depressed and released, then
Tech 2 indicate the Brake Pedal 1 Switch
parameter Applied when the brake pedal is
depressed and Released when the brake pedal is
released?

—

Go to Step 14

Go to Step 2

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

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