Content .. 906 907 908 909 ..

Isuzu N-Series. Manual - part 908

Transmission Control System (Smoother) 7A-87

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

7A-88 Transmission Control System (Smoother)

P0721 (Flash Code 26)

Circuit Description
The output shaft speed sensor that is called vehicle
speed sensor (VSS) is located on the transmission rear
housing and is used by the engine control module
(ECM), transmission control module (TCM) and
speedometer, which generates a speed signal from the
transmission output shaft. The output shaft speed
sensor uses a hall effect element. It interacts with the
magnetic field created by the rotating magnet and
outputs square wave pulse signal. The ECM calculates
the vehicle speed by the output shaft speed sensor and
calculated vehicle speed sent to the TCM via a controller
area network (CAN) communication bus. If the TCM
detects no output shaft speed sensor signal from the
ECM during the vehicle running, this DTC will set.
Condition for Running the DTC

• DTCs P0717, P0904, P0914 and U0100 are not

set.

• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The input shaft speed is more than 1500 RPM.
• The current gear is other than neutral.

Condition for Setting the DTC

• The TCM detects that the output shaft speed is

less than 30 RPM during the vehicle running.

Action Taken When the DTC Sets

• The TCM illuminates the transmission warning

lamp when the diagnostic runs and fails.

• The TCM inhibits auto shift control.
• The TCM selects highest gear when shifted from N

to D.

• The TCM inhibits gear select & shift position

learning and half-clutch learning.

Condition for Clearing the DTC

• The TCM turns OFF the transmission warning

lamp when the diagnostic runs and does not fail.

• A current DTC clears when the diagnostic runs and

does not fail.

• A history DTC clears when the diagnostic runs and

does not fail.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• Electrical or magnetic interference may affect

intermittent condition.

Notice:

• If this DTC is present, the Output Shaft Speed and

Vehicle Speed parameters on the Tech 2 will
indicate estimated value based on other inputs.

DTC P0721 (Flash Code 26)

Schematic Reference: Engine Controls Schematics
and Transmission Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views, Engine Control Module (ECM)
Connector End Views, Transmission Controls
Connector End Views or Transmission Control Module
(TCM) Connector End Views

Step

Action

Value(s)

Yes

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic

System Check -

Transmission

Controls

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

Information with the Tech 2.

Is DTC U0100, U0121 or U0406 set?

—

Go to Applicable

DTC

Go to Step 3

1. Select the “4HK1” in the system selection

menu.

2. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Is the engine control module (ECM) DTC P0500 or
P0501 set?

—

Go to Applicable

DTC in Engine

Control Section

Go to Step 4

1. Drive the vehicle.
2. Select the data display function of ECM.
3. Observe the Vehicle Speed parameter with the

Tech 2.

Does the Vehicle Speed parameter indicate correct
vehicle speed?

—

Go to Diagnostic

Aids

Go to Step 5

Transmission Control System (Smoother) 7A-89

1. Turn OFF the ignition.
2. Inspect the Meter (10A) fuse (F-16) in the

glove box fuse block.

Is the Meter (10A) fuse (F-16) open?

—

Go to Step 6

Go to Step 7

Replace the Meter (10A) fuse (F-16). If the fuse
continues to open, repair the short to ground on one
of the circuits that fed by the Meter (10A) fuse (F-
16) or replace the shorted attached component fed
by the Meter (10A) fuse (F-16).

Did you complete the repair?

—

Go to Step 18

—

1. Remove the output shaft speed sensor. Refer

to Output Shaft Speed Sensor replacement in
the section.

2. Visually inspect the output shaft speed sensor

for the following conditions:

• Physical damage
• Being loose
• Improper installation
• For transmission output shaft teeth

damage

3. Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 8

1. Turn OFF the ignition.
2. Disconnect the output shaft speed sensor

harness connector.

3. Connect a test lamp between the ignition

voltage feed circuit of the output shaft speed
sensor harness (pin 1 of J-32 connector) and a
known good ground.

4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 9

Go to Step 11

1. Keep the ignition switch ON.
2. Connect a test lamp between the low

reference circuit of the output shaft speed
sensor harness (pins 2 of J-32 connector) and
battery voltage.

Does the test lamp illuminate?

—

Go to Step 10

Go to Step 12

1. Turn ON the ignition, with the engine OFF.
2. Intermittently jump the signal circuit of the

output shaft speed sensor (pin 3 of J-32
connector) with a test lamp that is connected
to 12 volts (apply form a battery) while
monitoring the Vehicle Speed parameter with
the Tech 2.

Does the Tech 2 indicate any vehicle speed when
the circuit is intermittently pulled to 12 volts?

—

Go to Step 14

Go to Step 13

Repair the open circuit or high resistance on the
output shaft speed sensor ignition voltage feed
circuit between the output shaft speed sensor (pin 1
of J-32 connector) and the Meter (10A) fuse (F-16).

Did you complete the repair?

—

Go to Step 18

—

Step

Action

Value(s)

Yes

7A-90 Transmission Control System (Smoother)

Repair the open or high resistance in the output
shaft speed sensor low reference circuit between
the output shaft speed sensor (pin 2 of J-32
connector) and ground terminal.

Did you complete the repair?

—

Go to Step 18

—

1. Test the output shaft speed sensor signal

circuit between the engine control module
(ECM) (pin 19 of J-191 connector) and the
output shaft speed sensor (pin 3 of J-32
connector), then between the instrument panel
cluster (IPC) (pin 17 of B-52 connector) and
the output shaft speed sensor (pin 3 of J-32
connector) for the following conditions:

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

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 15

1. Turn OFF the ignition.
2. Disconnect the output shaft speed sensor

harness connector.

3. Inspect for an intermittent and for poor

connections at the harness connector of the
output shaft speed sensor (pin 1, 2 and 3 of J-
32 connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 16

1. Turn OFF the ignition.
2. Disconnect the ECM J-191 harness connector.
3. Inspect for an intermittent and for a poor

connection on the output shaft speed sensor
signal circuit at the harness connector of the
ECM (pin 19 of J-191 connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 17

Replace the output shaft speed sensor. Refer to
Output Shaft Speed Sensor Replacement in this
section.

Did you complete the replacement?

—

Go to Step 18

—

Important:
Replacement ECM must be programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement /Restore Fuel Injector ID Code
Data in engine control section.

Did you complete the replacement?

—

Go to Step 18

—

Step

Action

Value(s)

Yes

Content .. 906 907 908 909 ..