Isuzu KB P190. Manual — part 311

6E-210 Engine Control System (4JH1)

DTC P1520 (Symptom Code A) (Flash Code 47)

Circuit Description
(Manual Transmission)
The neutral switch is installed on the transmission gear
control box. When the gear position is neutral, the
switch is closed and the switch signal is provided to the
engine control module (ECM). If the ECM detects the
neutral switch signal is not changed from neutral during
the predetermined engine speed and vehicle speed
range, this DTC will set.
(Automatic Transmission)
The inhibitor switch is installed to the transmission case.
When the selector position is P or N range, the switch is
closed and the switch signal is provided to the Emir the
ECM detects the neutral switch signal is not changed
from P or N during the predetermined engine speed and
vehicle speed range, this DTC will set.
Condition for Running the DTC

• The ignition switch is ON.
• The engine speed is higher than 1500 RPM.
• The vehicle speed is higher than 63 km/h (39

MPH) (M/T) or 78 km/h (49 MPH) (A/T).

• The clutch pedal is released. (M/T).

Condition for Setting the DTC

• The ECM detects that the neutral switch signal is

continuously ON (neutral or P/N range) during
three consecutive driving cycles.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

Condition for Clearing the MIL/DTC
Important:

• Following conditions must be met two consecutive

driving cycles. (One driving cycle: Ignition switch
ON > Engine run > Vehicle run > Ignition switch
OFF for 10 seconds)
- The engine speed is higher than 1500 RPM
- The vehicle speed is higher than 63 km/h (39

MPH) (M/T) or 78 km/h (49 MPH) (A/T)

- The clutch pedal is released (M/T)

- Other than neutral or P/N range

- After the above procedure is done, 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 P1520 (Symptom Code A) (Flash Code 47)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Chart for M/T

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 ON the ignition, with the engine OFF.
3. Observe the Neutral Switch parameter with the

scan tool while shift to neutral and other
positions.

Does the scan tool indicate ON when the position is
neutral and OFF when other than the neutral?



Go to Diagnostic

Aids

Go to Step 3

3

1. Turn OFF the ignition.
2. Disconnect the neutral switch harness connector.
3. Turn ON the ignition, with the engine OFF.
4. Observe the Neutral Switch parameter with the

scan tool.

Does the scan tool indicate ON?



Go to Step 4

Go to Step 5

4

1. Test the neutral switch input signal circuit

between the engine control module (ECM) (pin
87 of C-57 connector) and the neutral switch (pin
1 of E-11 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 7

Go to Step 6

Engine Control System (4JH1) 6E-211

Step Action

Value(s)

Yes

No

5

Replace the neutral switch. Refer to Neutral Switch
Replacement in Transmission Section.
Did you complete the replacement?



Go to Step 7



6

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



7

1. Reconnect all previously disconnected harness

connector(s).

2. Clear the DTCs with the scan tool.
Important: Following conditions must be met two
consecutive driving cycles before clear with the scan
tool. (One driving cycle: Ignition switch ON > Engine
run > Vehicle run > Ignition switch OFF for 10
seconds)

• The engine speed is higher than 1500 RPM
• The vehicle speed is higher than 63 km/h

(39 MPH)

• The clutch pedal is released
• Other than neutral

3. Turn ON the ignition, with the engine OFF.
4. Observe the Neutral Switch parameter with the

scan tool while shift to neutral and other
positions.

Does the scan tool indicate ON when the position is
neutral and OFF when other than the neutral?



Go to Step 8

Go to Step 3

8

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

Chart for A/T

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. Turn ON the ignition, with the engine OFF.
4. Select the “JR405E Automatic Transmission” in

the system selection menu.

5. Monitor the Read Diagnostic Trouble Code

(DTC) Info As Stored By ECU with the scan tool.

Does the transmission control module (TCM) DTC
P0705 set?



Go to Applicable

DTC in Automatic

Transmission

Section

Go to Step 3

3

1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Observe the Neutral Switch parameter with the

scan tool while shift to P or N and other
positions.

Does the scan tool indicate ON when the position is
P or N and OFF when other than the P or N?



Go to Diagnostic

Aids

Go to Step 4

6E-212 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

4

1. Check to ensure the inhibitor switch is adjusted

correctly.

2. Adjust the inhibitor switch as necessary. Refer to

Inhibitor Switch Adjustment in Automatic
Transmission Section.

Did you find and correct the condition?



Go to Step 7

Go to Step 5

5

1. Test the P & N position switch signal circuit

between the engine control module (ECM) (pin
87 of C-57 connector) and the diode (pin 2 of X-
16 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 7

Go to Step 6

6

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



7

1. Reconnect all previously disconnected harness

connector(s).

2. Clear the DTCs with the scan tool.
Important: Following conditions must be met two
consecutive driving cycles before clear with the scan
tool. (One driving cycle: Ignition switch ON > Engine
run > Vehicle run > Ignition switch OFF for 10
seconds)

• The engine speed is higher than 1500 RPM
• The vehicle speed is higher than 78 km/h

(49 MPH)

• Other than P/N range

3. Turn ON the ignition, with the engine OFF.
4. Observe the Neutral Switch parameter with the

scan tool while shift to P or N and other
positions.

Does the scan tool indicate ON when the position is
P or N and OFF when other than the P or N?



Go to Step 8

Go to Step 2

8

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-213

DTC P1520 (Symptom Code B) (Flash Code 47)

Circuit Description
The neutral switch is installed on the transmission gear
control box. When the gear position is neutral, the
switch is closed and the switch signal is provided to the
engine control module (ECM). If the ECM detects the
neutral switch signal is not changed from other than
neutral during the predetermined engine speed and
vehicle speed range, this DTC will set. This DTC runs
only manual transmission.
Condition for Running the DTC

• The ignition switch is ON.
• The engine speed is higher than 665 RPM
• The vehicle speed is lower than 2 km/h (1.2 MPH).
• The clutch pedal is released after once depressed.

Condition for Setting the DTC

• The ECM detects that the neutral switch signal is

continuously OFF (other than neutral) during three
consecutive driving cycles.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

Condition for Clearing the MIL/DTC
Important:

• Following conditions must be met two consecutive

driving cycles. (One driving cycle: Ignition switch
ON > Engine run > Ignition switch OFF for 10
seconds)
- The engine speed is higher than 665 RPM
- The vehicle speed is lower than 2 km/h (1.2

MPH)

- The clutch pedal is released after once

depressed

- Neutral

position

- After the above procedure is done, 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 P1520 (Symptom Code B) (Flash Code 47)
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 ON the ignition, with the engine OFF.
3. Observe the Neutral Switch parameter with the

scan tool while shift to neutral and other
positions.

Does the scan tool indicate ON when the position is
neutral and OFF when other than the neutral?



Go to Diagnostic

Aids

Go to Step 3

3

1. Turn OFF the ignition.
2. Inspect the ECM (10A) fuse (EB-4) in the engine

room fuse block.

Is the ECM (10A) fuse (EB-4) open?



Go to Step 4

Go to Step 5

4

Replace the ECM (10A) fuse (EB-4). If the fuse
continues to open, repair the short to ground on one
of the circuits that is fed by the ECM (10A) fuse (EB-
4) or replace the shorted attached component fed by
the ECM (10A) fuse (EB-4).
Did you complete the repair?



Go to Step 13

