Isuzu N-Series. Manual - part 909

Transmission Control System (Smoother) 7A-91

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. Drive the vehicle.
5. Select the data display function of ECM.
6. Observe the Vehicle Speed parameter with the

Tech 2.

Does the Vehicle Speed parameter indicate correct
vehicle speed?

—

Go to Step 19

Go to Step 5

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-92 Transmission Control System (Smoother)

P0726 (Flash Code 16)

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 detects the actual state of
the lock up clutch solenoid valve by the slip speed of the
lock up clutch based on the engine speed and turbine
speed sensor signal inputs. If the TCM detects an
excessively low turbine speed in comparison to engine
speed, this DTC will set.
Condition for Running the DTC

• DTCs P0715, P0740, P0742 and U0400 are not

set.

• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.

Condition for Setting the DTC

• The TCM detects that the turbine speed is less

than the engine speed 300 RPM or more when the
lock up clutch is commanded engage.

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 when the diagnostic runs and

does not fail.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• Ensure the turbine speed sensor is tight and the

gearshift multi-plate clutch case is not damaged.

• If this DTC is present, lock up clutch slipping feel

will appear.

DTC P0726 (Flash Code 16)

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. Inspect for correct ATF level. Refer to ATF

inspection in this section.

2. Inspect for external leakage.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 3

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 within the Conditions for

Running the DTC.

5. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Is DTC P0715, P0740, P0742 or U0400 set?

—

Go to Applicable

DTC

Go to Step 4

1. Let the vehicle run so that lock up may operate

enough.

2. Observe the Engine Speed and Turbine

Speed parameter with the Tech 2.

Is the Turbine Speed parameter less than the
Engine Speed 300 RPM or more?

—

Go to Step 5

Go to Diagnostic

Aids

Transmission Control System (Smoother) 7A-93

Test the line pressure. Refer to line pressure test in
this section.

Does the line pressure within the specified value?

—

Go to Step 7

Go to Step 6

1. Inspect oil strainer for clogging. Repair

Instructions (Overhaul) - Oil Filter in this
section.

2. Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 8

1. Remove the turbine speed sensor. Refer to

Turbine Speed Sensor Replacement in this
section.

2. Visually inspect the turbine speed sensor for

the following conditions:

• Physical damage
• Loose or improper installation

3. The following conditions may cause this DTC

to set:

• Excessive air gap between the turbine

speed sensor and the gearshift multi-plate
clutch case

• Electromagnetic interference in the turbine

speed sensor circuits

• Foreign material passing between the

turbine speed sensor and the gearshift
multi-plate clutch case

4. Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 8

1. Remove the oil pump assembly. Refer to

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

2. Inspect the oil pump and gearshift clutch for

the following conditions:

• The oil pump for damage
• The lock up clutch solenoid valve for

mechanically stuck or leaking

• The lock up clutch spool valve

mechanically stuck or leaking

• The gasket or seal leaking or worn
• The gearshift multi-plate clutch for damage

3. Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 9

Replace the fluid coupling assembly. Refer to
Repair Instructions (Overhaul) - Fluid Coupling
Replacement in this section.

Did you complete the replacement?

—

Go to Step 10

—

Step

Action

Value(s)

Yes

7A-94 Transmission Control System (Smoother)

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. Lift the driving wheels or drive the vehicle.
5. Let the vehicle run so that lock up may operate

enough.

6. Observe the Engine Speed and Turbine

Speed parameter with the Tech 2.

Is the Turbine Speed parameter less than the
Engine Speed 300 RPM or more?

—

Go to Step 2

Go to Step 11

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

Content .. 907 908 909 910 ..