Isuzu N-Series. Manual - part 903

 

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Isuzu N-Series. 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

 

 

 

 

 

 

 

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