Isuzu N-Series. Service manual - part 918

Transmission Control System (Smoother) 7A-127

P0909 (Flash Code 76)

Circuit Description
The pulse width modulation (PWM) select solenoid
valve is located on the gearshift control box. The
transmission control module (TCM) controls the select
solenoid valve 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 gear select position sensor is
used to detect the select side lever position feedback for
the select solenoid valve movement. The TCM uses the
gear select position sensor to determine the current
gear position with a combination of the gear shift
position sensor. If the TCM detects the gear select side
lever position does not reach to a desired select position
when shifting to desired gear, this DTC will set.
Condition for Running the DTC

• DTCs P0718, P0889, P0902, P0903, P0904,

P0912, P0913, P0914, P0973, P0974, P0976 and
P0977 are not set.

• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The gearshift control box relay is commanded ON.
• The selector lever is other than N position.

Condition for Setting the DTC

• The TCM detects the gear select side lever

position does not reach to a desired select position
continuously when shifting to desired gear.

Action Taken When the DTC Sets

• The TCM illuminates the transmission warning

lamp when the diagnostic runs and fails.

• The TCM inhibits gearshift control.
• The TCM commands OFF the gearshift clutch

solenoid valve.

• The TCM commands OFF the lock up clutch

solenoid valve.

• 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.

DTC P0909 (Flash Code 76)

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

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. Lift the driving wheels or drive the vehicle.
4. Let the vehicle run so that all gear may engage

enough.

5. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Is P0902, P0903, P0904, P0912, P0913, P0914,
P0973, P0974, P0976 or P0977 also set?

—

Go to Applicable

DTC

Go to Step 3

Visually inspect the gear select position sensor and
the select solenoid valve for the following
conditions:
• Physical damage
• Loose or improper installation

Did you find and correct the condition?

—

Go to Step 8

Go to Step 4

7A-128 Transmission Control System (Smoother)

1. Lift the driving wheels or drive the vehicle.
2. Let the vehicle run so that all gear may engage

enough.

3. Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 5

Go to Diagnostic

Aids

If the DTC fail only when shifting from 5th to 6th with
the 5th speed transmission, programmed
transmission type is incorrect. Reprogram correct
vehicle information and retest. Refer to
Transmission Control Module (TCM) Replacement
Procedure Description in this section.

Did you find and correct the condition?

—

Go to Step 8

Go to Step 6

1. Remove the gear select position sensor. Refer

to Gear Select Position Sensor Replacement
in this section.

2. Visually inspect the gear select position sensor

for the following conditions:

• Physical damage
• Loose or improper installation

3. Inspect the gear select position sensor output

voltage in order to check an open circuit, short
circuit and high resistance somewhere in the
operating range.

4. Remove the transmission gearshift control box

assembly from the transmission main unit.
Refer to Repair Instructions (Overhaul) -
Control Box in this section.

5. Visually inspect the select side lever for the

following conditions:

• Select lever damage that connects to the

gear select position sensor shaft.

• Select lever damage that connects to the

interlock plate and shift rods.

• Select relay lever damage that connects to

the select solenoid valve.

• Other damage that the select lever

possible stuck.

6. Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 8

Go to Step 7

Important:
Replacement select solenoid valve must be learned.
Replace the select solenoid valve. Refer to Repair
Instructions (Overhaul) - Gearshift Control Box in
this section.

Did you complete the replacement?

—

Go to Step 8

—

Step

Action

Value(s)

Yes

Transmission Control System (Smoother) 7A-129

1. Reconnect all previously disconnected

harness connector(s).

2. Clear the DTCs with the Tech 2.

Important:
Transmission Gear Select & Shift Position Learning
must be done if the gear select position sensor,
select solenoid valve or transmission gearshift
control box is replaced, removed or repaired.

3. Turn OFF the ignition for 30 seconds.
4. Lift the driving wheels or drive the vehicle.
5. Let the vehicle run so that all gear may engage

enough.

6. Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 2

Go to Step 9

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-130 Transmission Control System (Smoother)

P0912 (Flash Code 75)

Circuit Description
The pulse width modulation (PWM) select solenoid
valve is located on the gearshift control box. The
transmission control module (TCM) controls the select
solenoid valve 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 gear select position sensor is
used to detect the select side lever position feedback for
the select solenoid valve movement. The TCM uses the
gear select position sensor to determine the current
gear position with a combination of the gear shift
position sensor. If the TCM detects a high voltage
condition on the select solenoid valve monitor circuit
when the solenoid valve is commanded OFF, this DTC
will set.
Condition for Running the DTC

• DTC P0889 is not set.
• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The gearshift control box relay is commanded ON.

Condition for Setting the DTC

• The TCM detects a high voltage condition on the

select solenoid valve monitor circuit when the
solenoid valve is commanded OFF.

Action Taken When the DTC Sets

• The TCM illuminates the transmission warning

lamp when the diagnostic runs and fails.

• The TCM intermittently sounds buzzer when the

diagnostic runs and fails.

• The TCM commands OFF gearshift control box

relay.

• The TCM inhibits gearshift control and holds gear

position when the diagnostic runs and fails.

• 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 at
next ignition cycle

• The TCM stops the buzzer when the diagnostic

runs and does not fail at next ignition cycle.

• A current DTC clears when the diagnostic runs and

does not fail at next ignition cycle.

• A history DTC clears with the Tech 2 or reset

switch operation.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

DTC P0912 (Flash Code 75)

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

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. Turn ON the ignition, with the engine OFF.
4. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Is DTC P0889 also set?

—

Go to DTC P0889

Go to Step 3

1. Turn OFF the ignition for 30 seconds.
2. Disconnect the select solenoid valve harness

connector.

3. Connect a DMM between the control circuit of

the select solenoid valve harness (pin 2 of J-
234 connector) and a known good ground.

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

Is the DMM voltage more than the specified value
until this DTC fails?

18.0 volts

Go to Step 4

Go to Step 6

Is the DMM voltage more than the specified value
after this DTC fails?

18.0 volts

Go to Step 7

Go to Step 5

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