Isuzu N-Series. Manual - part 911

Transmission Control System (Smoother) 7A-99

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 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 lock up clutch

solenoid valve between the lock up clutch
solenoid valve and the in-line harness
connector (pin 2 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

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

enough.

6. 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-100 Transmission Control System (Smoother)

P0851 (Flash Code 6)

Circuit Description
The neutral switch is installed on the transmission
gearshift control box. When the gear position is neutral,
the switch is closed and the switch signal is provided to
the transmission control module (TCM). If the TCM
detects the neutral switch signal is stuck OFF (open)
when the current gear is neutral based on the gear shift
position sensor input.
Condition for Running the DTC

• DTC P0914 is 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 neutral switch signal is

continuously OFF (other than neutral) when the
current gear is neutral.

Action Taken When the DTC Sets

• The TCM does not illuminate 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

• 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 gear shift position sensor is tight and

the sensor shaft is not damaged.

Notice:

• If this DTC is present, engine will not crank except

applying the brake pedal or parking brake.

DTC P0851 (Flash Code 6)

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.

Notice:
If the engine does not crank, apply the brake pedal
or parking brake.

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

enough.

6. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Is DTC P0914, P0915 or P0919 also set?

—

Go to Applicable

DTC

Go to Step 3

Observe the Neutral Switch parameter with the
Tech 2 while changing the gear between neutral
and other positions.

Does the Tech 2 indicate Neutral when the current
gear is neutral and In Gear when other than the
neutral?

—

Go to Diagnostic

Aids

Go to Step 4

Transmission Control System (Smoother) 7A-101

1. Turn OFF the ignition.
2. Disconnect the neutral switch harness

connector.

3. Turn ON the ignition, with the engine OFF.
4. Observe the Neutral Switch parameter with the

Tech 2 while momentarily jumping across the
neutral switch harness connectors between
pins 1 and 2 of J-50 connector.

Does the Tech 2 indicate Neutral when the circuit is
jumped and In Gear when the circuit is not jumped?

—

Go to Step 8

Go to Step 5

1. Connect a test lamp between the ignition

voltage feed circuit of the neutral switch
harness (pin 2 of J-50 connector) and a known
good ground.

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

Does the test lamp illuminate?

—

Go to Step 7

Go to Step 6

Repair the open circuit or high resistance on the
voltage feed circuit between the ENG (IG) (10A)
fuse (F-9) (in the glove box fuse block) and the
neutral switch (pin 2 of J-50 connector). Check the
ENG (IG) (10A) fuse (F-9) first.

Did you complete the repair?

—

Go to Step 13

—

1. Test the neutral switch signal circuit between

the transmission control module (TCM) (pin 10
of B-428 connector) and the neutral switch (pin
1 of J-50 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 13

Go to Step 9

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

connections at the harness connectors of the
neutral switch (pins 1 and 2 of J-50 connector).

3. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10

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

connection on the neutral switch circuit at the
harness connector of the TCM (pin 10 of B-428
connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

Step

Action

Value(s)

Yes

7A-102 Transmission Control System (Smoother)

1. Remove the neutral switch. Refer to Neutral

Switch Replacement in this section.

2. Visually inspect the neutral switch for the

following conditions:

• Physical damage
• Loose or improper installation

3. Remove the gear shift position sensor. Refer

to Gear Shift Position Sensor Replacement in
this section.

4. Visually inspect the gear shift position sensor

for the following conditions:

• Physical damage
• Loose or improper installation

5. Visually inspect the shift lever shaft to the gear

shift position sensor shaft for damage.

6. Remove the transmission gearshift control box

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

7. Visually inspect the neutral position detection

lever for damage that contacts to the neutral
switch.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

Replace the neutral switch. Refer to Neutral Switch
Replacement in this section.

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.

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

3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Observe the Neutral Switch parameter with the

Tech 2 while changing gear between neutral
and other positions.

Does the Tech 2 indicate Neutral when the current
gear is neutral and In Gear when other than the
neutral?

—

Go to Step 14

Go to Step 2

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

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