Isuzu Trooper (1998-2002 year). Manual - part 626

6E–152

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0502 (Flash DTC 24) 

VSS (Vehicle Speed Sensor) No Signal

060RW136

Circuit Description

The vehicle speed sensor has a magnet rotated by the
transmission output shaft.  Attached to the sensor is a hall
effect circuit the interacts with the magnetic field treated
by the rotating magnet.  A 12-volt operating supply for the
speed sensor hall circuit is supplied from the meter fuse.
The VSS pulses to ground the 9-volt signal sent from the
engine control module (ECM) on the reference circuit.
The ECM interprets vehicle speed by the number of
pulses to ground per second on the reference circuit.

Action Taken When the DTC Sets

D

The ECM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.

D

The ECM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.

Conditions for Clearing the MIL/DTC

D

DTC P0502 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

6E–153

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
10. To avoid backprobing the VSS and possibly

damaging a seal or terminal, the VSS output can be
tested at the point where the transmission harness
connected to the engine harness. The green 16-way
connector is adjacent to a blue 16-way connector,
and it can be easily accessed by removing the air
cleaner assembly.  The green 16-way connector is
separated, and battery voltage is applied to the VSS
through the yellow wire at one corner of the
connector.  The VSS output can be monitored with a
DVM connected to the blue wire with a black tracer.
The two wires are next to each other in the 16-way
connector .  The test connections are made on the
transmission side of the connector, the side that is
not clipped to the body sheetmetal.

11. The speedometer-to-ECM VSS signal wire is

spliced to a wire leading to the cruise control
module.  If a short to ground or voltage is found
between the ECM and speedometer, it could be
located between the splice and the cruise control
module.

DTC P0502 –VSS No Signal

 

Step

Action

Value(s)

Yes

No

1

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

—

Go to 

Step 2

Go to 

OBD

System

Check

2

Does the speedometer work?

—

Go to 

Step 10

Go to 

Step 3

3

1. Disconnect the VSS connector.
2. Ignition “ON.”
3. Using a test light to battery +, probe the connector

ground wire.

Did the light illuminate?

—

Go to 

Step 5

Go to 

Step 4

4

Repair the sensor ground.

Is the action complete?

—

Verify repair

—

5

1. Ignition “ON,” sensor disconnected.
2. Using a DVM, measure at the VSS connector

between ground and voltage supply.

Was the measurement near the specified value?

Battery

voltage

Go to 

Step 7

Go to 

Step 6

6

Repair the open or short to ground which may have
blown the meter fuse.

Is the action complete?

—

Verify repair

—

7

1. Ignition “ON,” VSS disconnected.
2. Using a DVM, measure at the VSS connector

between ground and the blue/black wire from the
speedometer.

Was the measurement near the specified value?

7.5-8 V

Go to 

Step 9

Go to 

Step 8

8

Check for an open or short circuit between the
speedometer and the VSS.

Was an open or short circuit located?

—

Verify repair

Go to 

Step 9

9

Replace the VSS.

Is the action complete?

—

Verify repair

Go to 

Step 10

10

Replace the speedometer.

Is the action complete?

—

Verify repair

Go to 

Step 11

6E–154

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

DTC P0502 –VSS No Signal

  (Cont'd)

Step

No

Yes

Value(s)

Action

11

Check for an open or short between the ECM and the
speedometer.

Was a problem found?

—

Verify repair

Go to 

Step 12

12

Replace the ECM (Refer to the Data Programming in
Case of ECM change).

Is the action complete?

—

Verify repair

—

6E–155

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0510 (Flash DTC 75) 

Idle SW Malfunction, Open Circuit

060RW134

Circuit Description

The idle switch signal is used by the Engine Control
Module ECM for fuel control.

Action Taken When the DTC Sets

D

The ECM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.

D

The ECM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.

Conditions for Clearing the MIL/DTC

D

DTC P0510 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

Diagnostic Aids

Check for the following conditions:

D

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.

D

Damaged harness – Inspect the wiring harness for
damage.  If the harness appears to be OK, observe the
Idle SW display on the Tech 2 while moving connectors
and wiring harnesses related to the Idle SW.

If DTC P0510 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set.