Isuzu N-Series. Manual - part 914

Transmission Control System (Smoother) 7A-111

Replace the gearshift control relay.

Did you complete the replacement?

—

Go to Step 13

—

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 13

—

1. Reconnect all previously disconnected fuse or

harness connector(s).

2. Clear the DTCs with the Tech 2.
3. Turn OFF the ignition for 30 seconds.
4. Turn ON the ignition, with the engine OFF.
5. Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 14

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-112 Transmission Control System (Smoother)

P0902 (Flash Code 65)

Circuit Description
The gearshift clutch pulse width modulation (PWM)
solenoid valve is located on the oil pump assembly. It
controls the transmission fluid supply to the gearshift
clutch control spool valve. The transmission control
module (TCM) controls the gearshift clutch solenoid
valve by duty cycle signal based on vehicle running
condition. Since normally open type solenoid valve is
used, the gearshift clutch control spool valve moves by
the applied fluid pressure when the TCM turns OFF the
gearshift clutch solenoid valve under the certain
condition. Then the gearshift multi-plate clutch
engagement pressure circuit connects with the line
pressure circuit. At the same time, the gearshift multi-
plate clutch is engaged. The TCM monitors the gearshift
clutch solenoid valve operating status through the
feedback circuit. If the TCM detects a low voltage
condition on the gearshift clutch solenoid valve control
circuit when the solenoid valve is commanded ON, this
DTC will set.
Condition for Running the DTC

• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The smoother main relay is commanded ON.

Condition for Setting the DTC

• The TCM detects a low voltage condition on the

gearshift clutch solenoid valve control circuit when
the solenoid valve is commanded ON.

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 inhibits gearshift control.
• The TCM inhibits emergency gearshift control.
• 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.

• The TCM stops the buzzer when the diagnostic

runs and does not fail.

• A current DTC clears when the diagnostic runs and

does not fail.

• 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 P0902 (Flash Code 65)

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. Place the transmission in neutral and set the

parking brake.

4. Start the engine.
5. Operate the selector lever from N to D and D

to N.

6. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic

Aids

1. Turn OFF the ignition.
2. Disconnect the in-line harness connector (J-

237) near the starter motor.

3. Connect a DMM between the control circuit of

the gearshift clutch solenoid valve harness
(pin 3 of J-237 female connector) and a known
good ground.

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

Is the DMM voltage more than the specified value?

18.0 volts

Go to Step 5

Go to Step 4

Transmission Control System (Smoother) 7A-113

1. Test the control circuit of the gearshift clutch

solenoid valve between the transmission
control module (TCM) (pin 30 of B-425
connector) and the in-line harness connector
(pin 3 of J-237 connector) for a short to ground.

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 8

Go to Step 7

1. Remove the oil pump assembly. Refer to

Repair Instructions (Overhaul) - Oil Pump in
this section.

2. Test the control circuit of the gearshift clutch

solenoid valve between the gearshift clutch
solenoid valve and the in-line harness
connector (pin 3 of J-237 connector) for the
following conditions:

• A short to ground
• A short to the transmission fluid

temperature (TFT) sensor low reference
circuit

3. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 8

Go to Step 6

Important:
Replacement gearshift clutch solenoid valve must
be learned.
Replace the gearshift clutch solenoid valve. Refer to
Repair Instructions (Overhaul) - Oil Pump in this
section.

Did you complete the replacement?

—

Go to Step 8

—

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 8

—

1. Reconnect all previously disconnected

harness connector(s).

2. Clear the DTCs with the Tech 2.
3. Turn OFF the ignition for 30 seconds.
4. Place the transmission in neutral and set the

parking brake.

5. Start the engine.
6. Operate the selector lever from N to D and D

to N.

7. Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

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-114 Transmission Control System (Smoother)

P0903 (Flash Code 65)

Circuit Description
The gearshift clutch pulse width modulation (PWM)
solenoid valve is located on the oil pump assembly. It
controls the transmission fluid supply to the gearshift
clutch control spool valve. The transmission control
module (TCM) controls the gearshift clutch solenoid
valve by duty cycle signal based on vehicle running
condition. Since normally open type solenoid valve is
used, the gearshift clutch control spool valve moves by
the applied fluid pressure when the TCM turns OFF the
gearshift clutch solenoid valve under the certain
condition. Then the gearshift multi-plate clutch
engagement pressure circuit connects with the line
pressure circuit. At the same time, the gearshift multi-
plate clutch is engaged. The TCM monitors the gearshift
clutch solenoid valve operating status through the
feedback circuit. If the TCM detects a high voltage
condition on the gearshift clutch solenoid valve control
circuit when the solenoid valve is commanded OFF, this
DTC will set.
Condition for Running the DTC

• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The smoother main relay is commanded ON.

Condition for Setting the DTC

• The TCM detects a high voltage condition on the

gearshift clutch solenoid valve control 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 inhibits gearshift control and holds gear

position when the diagnostic runs and fails.

• The TCM inhibits emergency gearshift control.
• 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.

• The TCM stops the buzzer when the diagnostic

runs and does not fail.

• A current DTC clears when the diagnostic runs and

does not fail.

• 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 P0903 (Flash Code 65)

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. Place the transmission in neutral and set the

parking brake.

4. Start the engine.
5. Operate the selector lever from N to D and D

to N.

6. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic

Aids

1. Turn OFF the ignition.
2. Disconnect the in-line harness connector (J-

237) near the starter motor.

3. Connect a test lamp between the control circuit

of the gearshift clutch solenoid valve harness
(pin 3 of J-237 female connector) and a known
good ground.

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

Does the test lamp illuminate?

—

Go to Step 4

Go to Step 5

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