Isuzu KB P190. Manual - part 306

6E-190  Engine Control System (4JH1) 

DTC P1120 (Symptom Code 1) (Flash Code 21) 

Circuit Description 
The accelerator pedal position (APP) sensor is mounted 
on the intake throttle assembly. 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 ECM monitors the APP 
sensor signal for voltages outside the normal range of 
the APP sensor. If the ECM detects an excessively high
APP sensor 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 APP sensor signal 

voltage is more than 4.5 volts for 0.5 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 scan tool. 

Diagnostic Aids 

•  If an intermittent condition is suspected, refer to

Intermittent Conditions in this section. 

 
DTC P1120 (Symptom Code 1) (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 

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 scan tool. 
2.  Turn OFF the ignition for 30 seconds. 
3.  Start the engine. 
4. Monitor the Diagnostic Trouble Code (DTC) 

Information with the scan tool. 

Does the DTC fail this ignition? 

 

Go to Step 3 

Go to Diagnostic 

Aids 

3 

1.  Turn OFF the ignition. 
2.  Disconnect the accelerator pedal position (APP) 

sensor harness connector. 

3.  Turn ON the ignition, with the engine OFF. 
4.  Observe the Accelerator Pedal Position (APP) 

parameter with the scan tool. 

Does the APP parameter less than the specified 
value? 

1% 

Go to Step 4 

Go to Step 5 

4 

1.  Turn OFF the ignition. 
2.  Connect a test lamp between the low reference 

circuit of the APP sensor harness (pin 1 of E-22 
connector) and battery voltage. 

3.  Turn ON the ignition, with the engine OFF. 
Does the test lamp illuminate? 

 

Go to Step 11 

Go to Step 8 

5 

1.  Turn OFF the ignition. 
2.  Connect a DMM between the 5 volts reference 

circuit of the APP sensor harness (pin 3 of E-22 
connector) and a known good ground. 

3.  Turn ON the ignition, with the engine OFF. 
Is the DMM voltage more than the specified value? 

4.5 volts 

Go to Step 6 

Go to Step 9 

Engine Control System (4JH1)  6E-191 

Step Action 

Value(s) 

Yes 

No 

6 

Is the DMM voltage less than the specified value at 
step 5? 

5.5 volts 

Go to Step 7 

Go to Step 10 

7 

Important: The APP 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 38 of C-56 connector) and 
the APP sensor (pin 2 of E-22 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 15 

Go to Step 14 

8 

.  Test the low reference circuit between the 1ECM 

(pin 49 of C-56 connector) and the APP sensor 
(pin 1 of E-22 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 15 

Go to Step 12 

9 

1.  Test the 5 volts reference circuit between the 

ECM (pin 57 of C-56 connector) and the APP 
sensor (pin 3 of E-22 connector) for the following 
conditions: 

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

2.  Repair the circuit(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 15 

Go to Step 14 

10 

1.  Test the 5 volts reference circuit between the 

ECM (pin 57 of C-56 connector) and the APP 
sensor (pin 3 of E-22 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 15 

Go to Step 14 

11 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for a poor 

connection at the harness connector of the APP 
sensor (pin 1 of E-22 connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 15 

Go to Step 13 

12 

1.  Turn OFF the ignition. 
2.  Disconnect the ECM harness connector. 
3. Inspect for an intermittent and for a poor 

connection on the APP sensor circuit at the 
harness connector of the ECM (pin 49 of C-56 
connector). 

4.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 15 

Go to Step 14 

13 

Replace APP sensor. Refer to Accelerator Pedal 
Position (APP) Sensor Replacement in this section. 
Did you complete the replacement? 

 

Go to Step 15 

 

14 

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 15 

 

6E-192  Engine Control System (4JH1) 

Step Action 

Value(s) 

Yes 

No 

15 

1.  Reconnect all previously disconnected harness 

connector(s). 

2.  Clear the DTCs with the scan tool. 
3.  Turn OFF the ignition for 30 seconds. 
4.  Turn ON the ignition, with the engine OFF. 
5.  Fully depress and release the accelerator pedal 

many times. 

6.  Monitor the DTC Information with the scan tool. 
Did the DTC fail this ignition? 

 

Go to Step 3 

Go to Step 16 

16 

Observe the DTC Information with the scan tool. 
Are there any DTCs that you have not diagnosed? 

 

Go to Diagnostic 

Trouble Code (DTC) 

List System 

OK 

 
 
 

Engine Control System (4JH1)  6E-193 

DTC P1120 (Symptom Code 7) (Flash Code 21) 

Circuit Description 
The accelerator pedal position (APP) sensor is mounted 
on the intake throttle assembly. 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 provides 5 volts reference voltage through the
reference circuit to the APP sensor. The ECM monitors 
the voltage on the 5 volts reference circuit. If the ECM 
detects an excessively high APP sensor 5 volts
reference 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 APP sensor voltage

supply circuit is more than 5.2 volts for 0.5
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 scan tool. 

Diagnostic Aids 

•  If an intermittent condition is suspected, refer to

Intermittent Conditions in this section. 

 

DTC P1120 (Symptom Code 7) (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 

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 scan tool. 
2.  Turn OFF the ignition for 30 seconds. 
3.  Start the engine. 
4. Monitor the Diagnostic Trouble Code (DTC) 

Information with the scan tool. 

Does the DTC fail this ignition? 

 

Go to Step 3 

Go to Diagnostic 

Aids 

3 

1.  Test the 5 volts reference circuit between 1the 

engine control module (ECM) (pin 57 of C-56 
connector) and the accelerator pedal position 
(APP) sensor (pin 3 of E-22 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 5 

Go to Step 4 

4 

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 5 

 

5 

1.  Reconnect all previously disconnected harness 

connector(s). 

2.  Clear the DTCs with the scan tool. 
3.  Turn OFF the ignition for 30 seconds. 
4.  Turn ON the ignition, with the engine OFF. 
5.  Fully depress and release the accelerator pedal 

many times. 

6.  Monitor the DTC Information with the scan tool. 
Did the DTC fail this ignition? 

 

Go to Step 3 

Go to Step 6