Isuzu N-Series. Manual - part 930

Transmission Control System (Smoother) 7A-175

16

1. Turn OFF the ignition for 30 seconds.
2. Start the engine and operate the vehicle

checking for acceptable performance and
driveability.

3. Observe the transmission warning lamp, the

vehicle performance and the driveability.

Does the vehicle operate correctly, without any
transmission warning lamp illumination and without
any stored DTCs?

—

System OK

Go to Diagnostic 

Trouble Code (DTC) 

List or Symptom 

Charts

Step

Action

Value(s)

Yes

No

7A-176 Transmission Control System (Smoother)

Transmission Warning Lamp Always On

Circuit Description
Ignition voltage is supplied to the transmission warning
lamp via meter fuse. The transmission control module
(TCM) turns the transmission warning lamp ON by
grounding the lamp control circuit. 
Transmission Warning Lamp Operation
The transmission warning lamp is located on the
instrument panel cluster (IPC).
Transmission Warning Lamp Function

• The transmission warning lamp informs the driver

that a malfunction has occurred and the vehicle
should be taken in for service as soon as possible.

• The transmission warning lamp illuminates during

a bulb test. 

• A DTC will be stored if the transmission warning

lamp is requested by the TCM.

Transmission Waning Lamp Illumination

• The transmission warning lamp illuminates for

approximately 3 seconds when the ignition switch
is turned ON, with the engine OFF. 

• The transmission warning lamp remains

illuminated if the transmission control module
(TCM) detects a fault.

Transmission Warning Lamp Always On

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

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls

2

1. Turn OFF the ignition for 30 seconds.
2. Turn OFF the emergency switch. 
3. Turn ON the ignition, with the engine OFF.

Does the transmission warning lamp always remain
ON after 3 seconds passed?

—

Go to Step 3

Check for DTCs and 

if none exist Go to 

Intermittent 

Conditions

3

1. Turn OFF the ignition.
2. Disconnect the transmission control module

(TCM) harness connector (B-425 connector).

3. Turn ON the ignition, with the engine OFF.
4. Observe the transmission warning lamp.

Is the transmission warning lamp illuminated?

—

Go to Step 4

Go to Step 6

4

1. Remove the instrument panel cluster (IPC).
2. Disconnect the IPC harness connector (B-53

connector).

3. Test the transmission warning lamp control

circuit between the TCM (pin 11 of B-425
connector) and the IPC (pin 8 of B-53
connector) for a short to ground.

4. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 5

5

Replace the IPC. Refer to Instrument Panel Cluster
(IPC) Replacement in the Cab and Chassis
Electrical section.

Did you complete the replacement?

—

Go to Step 7

—

6

Important:
Replacement TCM must be programmed and
learned.
Replace the TCM. Refer to Transmission Control
Module (TCM) Replacement in this section.

Did you complete the replacement?

—

Go to Step 7

—

Transmission Control System (Smoother) 7A-177

7

1. Remove all test equipment.
2. Connect any disconnected components.
3. Turn ON the ignition, with the engine OFF.

Does the transmission warning lamp always remain
ON after 3 seconds passed?

—

Go to Step 2

Go to Step 8

8

1. Turn OFF the ignition for 30 seconds.
2. Start the engine and operate the vehicle

checking for acceptable performance and
driveability.

3. Observe the transmission warning lamp, the

vehicle performance, and the driveability.

Does the vehicle operate correctly, without any
transmission warning lamp illumination and without
any stored DTCs?

—

System OK

Go to Diagnostic 

Trouble Code (DTC) 

List or Symptom 

Charts

Step

Action

Value(s)

Yes

No

7A-178 Transmission Control System (Smoother)

Gearshift Control System Check

Description
The pulse width modulation (PWM) select solenoid
valve, 1-3-5 and 2-4-6-R shift solenoid valves are
located on the gearshift control box. The transmission
control module (TCM) controls each select and shift
solenoid valves by duty cycle signal based on
commanded gear position. The select solenoid is only
commanded ON when up-shifting. When downshifting,
the force created by the return springs moves the
internal select lever, but the select solenoid limits the
amount of movement by generating force as required in
the up-shift direction. The 1-3-5 shift solenoid is
commanded ON when the commanded gear is set to
1st, 3rd and 5th gear. When disengaging from 2nd, 4th,
6th and reverse gear, the 1-3-5 shift solenoid is also
commanded ON. The 2-4-6-R shift solenoid is
commanded ON when the commanded gear is set to
2nd, 4th, 6th and reverse gear. When disengaging
from1st, 3rd and 5th gear, the 2-4-6-R shift solenoid is
also commanded ON. The gear select position sensor is
used to detect the select side lever position feedback for
the select solenoid valve movement. The gear shift
position sensor is used to detect the shift side lever
position feedback for the shift solenoid valves
movement. The TCM uses the gear shift position sensor
to determine the current gear position with a
combination of the gear select position sensor. 
When the selector lever is in the N position, the
transmission is in neutral. Operating the lever to the R
position puts the vehicle into reverse. Operating the
lever to the D position puts the vehicle into drive, and
into auto shift mode. Operating the lever to the +
direction from D, shifts the up-shifting. Operating it to the

− direction, shifts the downshifting. This operation also
switches to the manual mode. Operating the lever from
the D position to the A position while in the manual mode
switches to the auto mode. When the selector lever is
moved to any of the A, + or 

− positions from the D

position, it will automatically return to the D position. 

The economy mode switch can be pressed during the
auto mode if you want gear changes to be performed
with the priority on efficient fuel consumption. The 1st
gear start switch is used to control vehicle starting so
that 1st gear is normally used to start vehicle. This is
because the transmission is controlled to start in 2nd
gear if the 1st gear start switch is not ON. 
The emergency switch, which is used when the TCM or
related switches or sensors fail and normal control is not
possible, and the emergency shift switch are located in
front of the selector lever. As these switches are only
used in an emergency, they are usually protected with a
cover.
The diagnostic table assumes the following conditions
are met:

• The battery is completely charged and terminals

are cleaned and tight.

• Fuse and slow blow fuse are normal. 
• The vehicle information data is correctly

programmed and transmission gear select & shift
position is correctly learned. 

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Gearshift Control System Check
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

Chart 1 of 4

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls