Isuzu N-Series. Manual - part 912

Transmission Control System (Smoother) 7A-103

P0852 (Flash Code 7)

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 ON (closed)
condition when the current gear is other than 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 ON (neutral) when the current gear is
other than 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 may not crank except

applying the brake pedal or parking brake.

DTC P0852 (Flash Code 7)

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

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.

Does the Tech 2 indicate In Gear?

—

Go to Step 6

Go to Step 5

7A-104 Transmission Control System (Smoother)

1. Test the neutral switch input 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 a
short to battery or ignition voltage.

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 8

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 9

Go to Step 7

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

Did you complete the replacement?

—

Go to Step 9

—

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 9

—

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 10

Go to Step 2

Step

Action

Value(s)

Yes

Transmission Control System (Smoother) 7A-105

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-106 Transmission Control System (Smoother)

P0885 (Flash Code 38)

Circuit Description
The smoother main relay is energized to feed the battery
voltage to the TCM through the relay switch side when
the TCM receives an ignition voltage switch ON signal.
When the ignition switch is OFF, the smoother main
relay is de-energized after a certain length of time
passed.
If the TCM detects the smoother main relay is turned
OFF when the relay is commanded ON, this DTC will
set. (Open stuck DTC)
If the TCM detects the TCM has been ON when the
relay is commanded OFF, this DTC will also set. (Close
stuck DTC)
Condition for Running the DTC

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

Condition for Setting the DTC
Open stuck DTC

• The TCM detects a low voltage condition on the

smoother main relay voltage feed circuit when the
relay is commanded ON.

Close stuck DTC

• The TCM detects a high voltage condition on the

smoother main relay voltage feed circuit when the
relay is commanded OFF.

Action Taken When the DTC Sets

• The TCM illuminates the transmission warning

lamp when the diagnostic runs and fails.

• The TCM continuously sounds buzzer when the

diagnostic runs and fails. (Open stuck DTC)

• The TCM inhibits gearshift control. (Open stuck

DTC)

• The TCM holds gear position.
• 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. (Open stuck DTC)

• 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.

• Faulty or sticking smoother main relay will set this

DTC.

DTC P0885 (Flash Code 38)

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.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic

Aids

1. Turn OFF the ignition for 30 seconds.
2. Replace the smoother main relay with the

dimmer relay or replace with a known good
relay.

3. Turn ON the ignition, with the engine OFF.
4. Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 4

Go to Step 11

1. Turn ON the ignition, with the engine OFF.
2. Observe the Main Relay Voltage Feed Circuit

parameter with the Tech 2.

Does the Main Relay Voltage Feed Circuit
parameter indicate ON?

—

Go to Step 8

Go to Step 5

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