Isuzu N-Series. Service manual — part 903

Transmission Control System (Smoother) 7A-67

P1901

19

OFF

OFF

Clutch
Adjustment
Switch (Fast)
Circuit

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The vehicle speed

is more than 5 km/h
(3 MPH).

• The TCM detects that

the half-clutch
adjustment fast switch
signal is stuck at the
ON position (high
voltage).

• Switch signal circuit is

short to battery or
ignition voltage.

• Faulty switch.
• Faulty TCM.

P1902

19

OFF

OFF

Clutch
Adjustment
Switch (Slow)
Circuit

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The vehicle speed

is more than 5 km/h
(3 MPH).

• The TCM detects that

the half-clutch
adjustment slow switch
signal is stuck at the
ON position (high
voltage).

• Switch signal circuit is

short to battery or
ignition voltage.

• Faulty switch.
• Faulty TCM.

U0100

42

ON

OFF

CAN-BUS Error

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The TCM detects that

the CAN Bus
messages are not
being received.

• CAN Low circuit is short

to battery or ignition
voltage, short to
ground, open circuit or
high resistance.

• CAN High circuit is

short to battery or
ignition voltage, short to
ground, open circuit or
high resistance.

• Faulty resistor 1.
• Faulty resistor 2.
• Faulty ECM.
• Faulty DRM.
• Faulty TCM.
• Faulty EHCU.
• Electromagnetic

interference and
electrical noise.

U0121

68

OFF

OFF

ABS Signal Line
Error

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The TCM detects that

the CAN Bus
messages from the
EHCU are not being
received.

• CAN Low circuit to the

EHCU is open circuit.

• CAN High circuit to the

EHCU is open circuit.

• Faulty resistor 1.
• Faulty resistor 2.
• Faulty ECM.
• Faulty EHCU.
• Electromagnetic

interference and
electrical noise.

DTC

Flash
Code

W/L

Status

Buzzer

Status

DTC Name

Condition for Running

the DTC

Condition for Setting the

DTC

Possible Cause

7A-68 Transmission Control System (Smoother)

U0400

23

ON

OFF

Engine Speed
Signal Error

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The TCM detects that

the engine speed CAN
Bus messages from the
ECM are not being
received.

• Faulty crankshaft

position sensor circuits.

• Faulty camshaft

position sensor circuits.

• CAN Low circuit is short

to battery or ignition
voltage, short to
ground, open circuit or
high resistance.

• CAN High circuit is

short to battery or
ignition voltage, short to
ground, open circuit or
high resistance.

• Faulty resistor 1.
• Faulty resistor 2.
• Faulty ECM.
• Faulty DRM.
• Faulty TCM.
• Faulty EHCU.
• Electromagnetic

interference and
electrical noise.

U0401

24

ON

OFF

Accelerator
Sensor Signal
Malfunction

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The TCM detects that

the accelerator pedal
position CAN Bus
messages from the
ECM are not being
received.

• Faulty accelerator

pedal position sensor
circuits.

• CAN Low circuit is short

to battery or ignition
voltage, short to
ground, open circuit or
high resistance.

• CAN High circuit is

short to battery or
ignition voltage, short to
ground, open circuit or
high resistance.

• Faulty resistor 1.
• Faulty resistor 2.
• Faulty ECM.
• Faulty DRM.
• Faulty TCM.
• Faulty EHCU.
• Electromagnetic

interference and
electrical noise.

DTC

Flash
Code

W/L

Status

Buzzer

Status

DTC Name

Condition for Running

the DTC

Condition for Setting the

DTC

Possible Cause

Transmission Control System (Smoother) 7A-69

U0406

25

ON

OFF

Vehicle Speed
Signal Error

• The ignition switch

is ON.

• The ignition voltage

is more than 20
volts.

• The emergency

switch is OFF.

• The TCM detects that

the vehicle speed CAN
Bus messages from the
ECM are not being
received.

• Faulty vehicle speed

sensor circuits.

• CAN Low circuit is short

to battery or ignition
voltage, short to
ground, open circuit or
high resistance.

• CAN High circuit is

short to battery or
ignition voltage, short to
ground, open circuit or
high resistance.

• Faulty resistor 1.
• Faulty resistor 2.
• Faulty ECM.
• Faulty DRM.
• Faulty TCM.
• Faulty EHCU.
• Electromagnetic

interference and
electrical noise.

DTC

Flash
Code

W/L

Status

Buzzer

Status

DTC Name

Condition for Running

the DTC

Condition for Setting the

DTC

Possible Cause

7A-70 Transmission Control System (Smoother)

P0602

Description
The transmission control module (TCM) has the ability
to set a diagnostic trouble code (DTC) if it detects that
there is no vehicle information programmed.
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 under certain

conditions.

Condition for Clearing the DTC

• The TCM blinks the transmission warning lamp

when the diagnostic runs and does not fail, and
turns OFF the transmission warning lamp when the
initial learning is completed.

• 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

Notice:

• Production and service TCM does not require

software programming when it is replaced except
calibration software update. This DTC indicates
that a production or service TCM did not program
vehicle information and learn.

DTC P0602

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic

System Check -

Transmission

Controls

2

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 Step 4

3

Program and learn the TCM. Refer to Transmission
Control Module (TCM) Replacement in this section.

Did you complete the programming?

—

Go to Step 4

—

4

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

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 5

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