Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 68

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–267

Check for the following conditions:

• Poor connection at ECM-Inspect harness connectors

for backed out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal to wire connection.

• Damaged harness-Inspect the wiring harness for

damage. If the harness appears to be OK, observe
the  “Neutral Switch” display on the Tech2 while
moving connectors and wiring harness related to the
sensor.

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

Neutral Switch ON Error

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

Neutral Switch OFF Error

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to Step 2

Go to On Board 

Diagnostic 

(OBD) System 

Check

2

1. Connect the Tech 2. 

2. Review and record the failure information. 

3. Select “F0: Read DTC Infor As Stored By ECU” in

“F0: Diagnostic Trouble Codes”. 

Is the DTC P1520 (Symptom Code A) or P1520
(Symptom Code B) stored as “Present Failure”?

—

Go to Step 3

Refer to 

Diagnostic Aids 

and Go to Step 

3

3

1. Using the Tech 2, ignition “On” and engine “Off”. 

2. Select  “F1: Clear DTC Information” in “F0:

Diagnostic Trouble Codes” with the Tech 2 and
clear the DTC information. 

3. Operate the vehicle and monitor the “F0: Read

DTC Infor As Stored By ECU” in the “F0:
Diagnostic Trouble Codes”. 

Was the DTC P1520 (Symptom Code A) or P1520
(Symptom Code B) stored in this ignition cycle?

—

Go to Step 4

Refer to 

Diagnostic Aids 

and Go to Step 

4

6E–268

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

4

Check for poor/faulty connection at the neutral switch
(inhibitor switch) or ECM connector. If a poor/faulty
connection is found, repair as necessary. 
Was the problem found?

—

Verify repair

Go to Step 5

5

Using the DVM and check the neutral switch (inhibitor
switch). 

1. Ignition “Off”, engine “Off”. 

2. Remove the neutral switch connector (inhibitor

switch connector) at the transmission. 

3. Check the neutral switch (P range  N range

switch). 

Was the DVM indicated specified value?

Neutral (P or 

N): Continuity

Other than 

neutral (P or 

N): No 

continuity Go 

to 

Step 6

Replace neutral 

switch (inhibitor 

switch) and 

verify repair

Step

Action

Value(s)

Yes

No

87

C-57

E-11

M/T

E-12

3

5

6

E-51

A/T

E-11

E-12

M/T

5

1

2

10

4

3

6

7

9

8

6

3

5

A/T

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–269

6

Using the DVM and check the neutral switch (inhibitor
switch) power supply circuit. 

1. Ignition “On”, engine “Off”. 

2. Remove the neutral switch (inhibitor switch)

connector from the switch. 

3. Check the circuit for open circuit. 

Was the DVM indicated specified value?

Battery 
voltage

Go to Step 8

Go to Step 7

7

Repair the open circuit between the ECM Main Relay
and neutral switch (between the “Back, Turn fuse
(15A)” and inhibitor switch). 
Is the action complete?

—

Verify repair

—

Step

Action

Value(s)

Yes

No

V

3

V

M/T

E-51

E-11

A/T

6E–270

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

8

Using the DVM and check the neutral switch (inhibitor
switch) circuit. 
Breaker box is available: 

1. Ignition “Off”, engine “Off”. 

2. Install the breaker box as type B. (ECM

connected) Ref. Page 6E-81 

3. Ignition “On”, engine “Off”. 

4. Check the circuit for open or short to voltage

circuit. 

Was the DVM indicated specified value?

Breaker box is not available: 

1. Ignition “On”, engine “Off”. 

2. Back probe the DVM to the neutral switch (inhibitor

switch) and check the circuit for open or short to
voltage circuit. 

Was the DVM indicated specified value?

Neutral (P or 

N): Battery 

voltage

Other than 

neutral (P or 

N): Less than 

1V Go 

to 

Step 11

Fixed at battery 

voltage: Go to 

Step 9

Fixed at less 

than 1V: Go to 

Step 10

9

Repair the short to voltage circuit between the neutral
switch connector (inhibitor switch connector) and
ECM. 
Is the action complete?

—

Verify repair

—

Step

Action

Value(s)

Yes

No

87

V

V

6

5

V

V

E-51

A/T

E-12

M/T

87

87

6

5

C-57

C-57

M/T

A/T

E-12

E-51