Isuzu N-Series. Service manual - part 910

Transmission Control System (Smoother) 7A-95

P0740 (Flash Code 67)

Circuit Description
The lock up clutch (ON/OFF) solenoid valve is located
on the oil pump assembly. It controls the transmission
fluid supply to the lock up clutch control spool valve. The
transmission control module (TCM) controls the lock up
solenoid valve by ON/OFF signal based on vehicle
running condition. The TCM turns ON the lock up
solenoid valve when the certain condition has been met.
Then the lock up clutch control spool valve moves by the
applied fluid pressure. The lock up engagement
pressure circuit connects with the line pressure circuit,
and the lock up clutch disengage pressure circuit
connects to the drain circuit. The lock up clutch
engagement pressure is nearly equal with the line
pressure. At the same time, the lock up clutch is pressed
to the fluid coupling front cover and then the fluid
coupling is locked. The TCM monitors the lock up clutch
solenoid valve operating status through the feedback
circuit. If the TCM detects a high voltage condition on
the lock up 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

lock up 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 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 with the Tech 2 or reset

switch operation.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• If this DTC is present, deteriorated vehicle starting

feel will appear.

DTC P0740 (Flash Code 67)

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. Start the engine.
4. 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 lock up clutch solenoid valve harness (pin
1 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 4

Go to Step 5

1. Connect a test lamp between the control circuit

of the lock up clutch solenoid valve harness
(pin 1 of J-237 female connector) and a known
good ground.

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

Does the test lamp illuminate?

—

Go to Step 6

Go to Step 7

7A-96 Transmission Control System (Smoother)

1. Test the control circuit of the lock up clutch

solenoid valve between the transmission
control module (TCM) (pin 29 of B-425
connector) and the in-line harness connector
(pin 1 of J-237 connector) for an open circuit or
high resistance.

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 8

1. Test the control circuit of the lock up clutch

solenoid valve between the TCM (pin 29 of B-
425 connector) and the in-line harness
connector (pin 1 of J-237 connector) for the
following conditions:

• A short to battery or ignition voltage
• A short to the gearshift clutch solenoid

valve control circuit

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 11

1. Turn OFF the ignition.
2. Inspect for an intermittent and for a poor

connection at the in-line harness connector
(pin 1 of J-237 connector).

3. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 9

1. Turn OFF the ignition.
2. Disconnect the TCM harness connector.
3. Inspect for an intermittent and for a poor

connection on the lock up clutch solenoid
valve circuit at the harness connector of the
TCM (pin 29 of B-425 connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 11

1. Remove the oil pump assembly. Refer to

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

2. Inspect for an intermittent and for a poor

connection at the harness connector of the
lock up clutch solenoid valve.

3. Inspect the lock up clutch solenoid valve for

loose bolt.

4. Test the control circuit of the lock up clutch

solenoid valve between the lock up clutch
solenoid valve and the in-line harness
connector (pin 1 of J-237 connector) for the
following conditions:

• An open circuit
• A short to the gearshift clutch solenoid

valve control circuit

• High resistance

5. Repair the circuit(s), connection(s) or tightness

as necessary.

Did you find and correct the condition?

—

Go to Step 12

Go to Step 10

Replace the lock up clutch solenoid valve. Refer to
Repair Instructions (Overhaul) - Oil Pump in this
section.

Did you complete the replacement?

—

Go to Step 12

—

Step

Action

Value(s)

Yes

Transmission Control System (Smoother) 7A-97

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 12

—

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. Start the engine.
5. Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 13

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-98 Transmission Control System (Smoother)

P0742 (Flash Code 67)

Circuit Description
The lock up clutch (ON/OFF) solenoid valve is located
on the oil pump assembly. It controls the transmission
fluid supply to the lock up clutch control spool valve. The
transmission control module (TCM) controls the lock up
solenoid valve by ON/OFF signal based on vehicle
running condition. The TCM turns ON the lock up
solenoid valve when the certain condition has been met.
Then the lock up clutch control spool valve moves by the
applied fluid pressure. The lock up engagement
pressure circuit connects with the line pressure circuit,
and the lock up clutch disengage pressure circuit
connects to the drain circuit. The lock up clutch
engagement pressure is nearly equal with the line
pressure. At the same time, the lock up clutch is pressed
to the fluid coupling front cover and then the fluid
coupling is locked. The TCM monitors the lock up clutch
solenoid valve operating status through the feedback
circuit. If the TCM detects a low voltage condition on the
lock up 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

lock up 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 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 with the Tech 2 or reset

switch operation.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• If this DTC is present, lock up clutch does not

engage and excessive slip feel will appear.

DTC P0742 (Flash Code 67)

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 lock up may operate

enough.

5. 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 lock up clutch solenoid valve harness (pin
1 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

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