Isuzu N-Series. Manual - part 901

Transmission Control System (Smoother) 7A-59

Diagnostic Trouble Code (DTC) List

DTC

Flash 
Code

W/L 

Status

Buzzer 

Status

DTC Name 

Condition for Running 

the DTC

Condition for Setting the 

DTC

Possible Cause

P0602

—

Blinks

Intermitten

tly ON

Control Module 
Not Programmed

—

• Vehicle information is 

not programmed.

• Vehicle information is 

not programmed and 
learned.

P0605

33

ON

Continuity 

ON

Control Module 
Internal 
Performance

—

Either of following 
condition is met:
• The TCM detects a 

malfunction in its 
internal Random 
Access Memory 
(RAM).

• The TCM detects a 

calculated checksum 
does not agree with the 
TCM internal registered 
checksum.

• Faulty TCM. 

P0613

33

ON

Continuity 

ON

Control Module 
EEPROM Error

—

• The TCM detects a 

faulty learning data in 
the Electronically 
Erasable 
Programmable Read 
Only Memory 
(EEPROM).

• Faulty TCM. 

P0710

21

ON

OFF

Transmission 
Fluid 
Temperature 
Sensor Circuit

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The TCM detects that 

the TFT sensor signal 
voltage is less than 0.1 
volts (more than 165

°C 

[329

°F]) or more than 

4.9 volts (less than

 

−

50

°C [−58°F]). 

• Sensor signal circuit is 

short to battery or 
ignition voltage or short 
to any 5V reference 
circuit, short to ground, 
short to the low 
reference circuit, open 
circuit or high 
resistance.

• Sensor low reference 

circuit is open circuit or 
high resistance.

• Poor harness 

connector connection.

• Faulty sensor. 
• Faulty TCM.

P0715

3

ON

OFF

Turbine Speed 
Sensor Circuit

• DTCs P0721, 

P0726, U0400 and 
U0406 are not set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The engine is 

running.

• The lock up clutch is 

commanded 
engage.

• The TCM detects that 

the turbine speed 
sensor pulses are not 
generated during lock 
up control.

• Faulty sensor 

installation condition. 

• Faulty sensor wheel 

(gearshift clutch case).

• Sensor signal circuit is 

short to battery or 
ignition voltage, short to 
any 5V reference 
circuit, short to ground, 
open circuit or high 
resistance.

• Sensor low circuit is 

open circuit or high 
resistance.

• Sensor circuits short to 

each other.

• Poor harness 

connector connection.

• Faulty sensor.
• Faulty TCM.
• Electromagnetic 

interference and 
electrical noise.

7A-60 Transmission Control System (Smoother)

P0717

2

ON

OFF

Input Speed 
Sensor Circuit

• DTCs P0715, 

P0718, P0721, 
P0726, U0400 and 
U0406 are not set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The engine is 

running.

• The turbine speed is 

more than 500 
RPM.

• The vehicle speed 

is more than 10 km/
h (6 MPH). 

• The gearshift clutch 

is commanded 
engage.

• The TCM detects that 

the input shaft speed 
sensor pulses are not 
generated during 
vehicle running.

• Faulty sensor 

installation condition.

• Faulty sensor wheel 

(counter shaft).

• Sensor signal circuit is 

short to battery or 
ignition voltage, short to 
any 5V reference 
circuit, short to ground, 
open circuit or high 
resistance.

• Sensor low circuit is 

open circuit or high 
resistance.

• Sensor circuits short to 

each other.

• Poor harness 

connector connection.

• Faulty sensor.
• Faulty TCM.
• Electromagnetic 

interference and 
electrical noise.

P0718

17

ON

OFF

Gearshift Clutch 
Slip Error

• DTCs P0715 and 

P0717 are not set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The TCM detects that 

the input shaft speed is 
less than the turbine 
speed 300 RPM or 
more when the 
gearshift clutch is 
commanded engage.

• Faulty ATF amount.
• Faulty line pressure 

(low).

• Faulty oil pump.
• Faulty gearshift clutch.
• Faulty gearshift clutch 

solenoid valve.

• Faulty gearshift clutch 

oil pressure circuits.

• Faulty band brake.
• Faulty input shaft 

speed sensor.

P0721

26

ON

OFF

Output Speed 
Sensor 
Performance

• DTCs P0717, 

P0904, P0914 and 
U0100 are not set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The input shaft 

speed is more than 
1500 RPM.

• The current gear is 

other than neutral.

• The TCM detects that 

the output shaft speed 
is less than 30 RPM 
during the vehicle 
running.

• Faulty sensor 

installation.

• Sensor voltage feed 

circuit is open circuit or 
high resistance.

• Sensor signal circuit is 

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

• Sensor low reference 

circuit is open circuit or 
high resistance.

• Poor harness 

connector connection.

• Faulty sensor.
• Faulty ECM.
• Faulty TCM.
• 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-61

P0726

16

ON

OFF

Lock Up Clutch 
Slip Error

• 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.

• 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.

• Faulty ATF amount.
• Faulty line pressure 

(low).

• Faulty oil pump.
• Faulty fluid coupling.
• Faulty lock up clutch 

solenoid valve.

• Faulty lock up clutch oil 

pressure circuits.

• Faulty turbine speed 

sensor.

P0740

67

ON

OFF

Lock Up Clutch 
Solenoid Circuit 
High Voltage

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The smoother main 

relay is commanded 
ON.

• The TCM detects a 

high voltage condition 
on the lock up clutch 
solenoid valve control 
circuit when the 
solenoid valve is 
commanded OFF.

• Solenoid valve control 

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

• Poor harness 

connector connection.

• Faulty solenoid valve.
• Faulty TCM.

P0742

67

ON

OFF

Lock Up Clutch 
Solenoid Circuit 
Low Voltage

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The smoother main 

relay is commanded 
ON.

• The TCM detects a low 

voltage condition on the 
lock up clutch solenoid 
valve control circuit 
when the solenoid 
valve is commanded 
ON.

• Solenoid valve control 

circuit is short ground. 

• Poor harness 

connector connection.

• Faulty solenoid valve.
• Faulty TCM.

P0851

6

OFF

OFF

Neutral Switch 
Circuit Low 
Voltage

• DTC P0914 is not 

set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The TCM detects that 

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

• Switch voltage feed 

circuit is open circuit or 
high resistance.

• Switch signal circuit is 

open circuit or high 
resistance.

• Poor harness 

connector connection.

• Faulty switch 

installation.

• Faulty gearshift control 

box internal lever.

• Faulty switch
• Faulty gear shift 

position sensor.

• Faulty 1-3-5 shift 

solenoid.

• Faulty 2-4-6-R shift 

solenoid.

• Faulty TCM.

DTC

Flash 
Code

W/L 

Status

Buzzer 

Status

DTC Name 

Condition for Running 

the DTC

Condition for Setting the 

DTC

Possible Cause

7A-62 Transmission Control System (Smoother)

P0852

7

OFF

OFF

Neutral Switch 
Circuit High 
Voltage

• DTC P0914 is not 

set.

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The TCM detects that 

the neutral switch 
signal is continuously 
ON (neutral) when the 
current gear is other 
than neutral.

• Switch signal circuit is 

short to battery or 
ignition voltage.

• Poor harness 

connector connection.

• Faulty switch 

installation.

• Faulty gearshift control 

box internal lever.

• Faulty switch
• Faulty gear shift 

position sensor.

• Faulty 1-3-5 shift 

solenoid.

• Faulty 2-4-6-R shift 

solenoid.

• Faulty TCM.

P0885

38

ON

Continuity 

ON (Open 

Stuck 

DTC)/ OFF 

(Close 

Stuck 
DTC)

TCM Power 
Relay Control 
Circuit

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts. 

• The emergency 

switch is OFF.

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.

• Relay power feed 

circuit is open circuit or 
high resistance.

• Relay control circuit is 

short to ground, open 
circuit or high 
resistance.

• Relay voltage feed 

circuit is short to 
battery, open circuit or 
high resistance.

• Poor harness 

connector connection.

• Faulty relay.
• Faulty TCM.

P0889

39

ON

Continuity 

ON (Open 

Stuck 

DTC)/ OFF 

(Close 

Stuck 
DTC)

Gearshift Relay 
Control Circuit

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts. 

• The emergency 

switch is OFF.

Open stuck DTC
• The TCM detects a low 

voltage condition on the 
1-3-5 shift solenoid, 2-
4-6-R shift solenoid and 
select solenoid voltage 
feed circuit when the 
gearshift control box 
relay is commanded 
ON.

Close stuck DTC
• The TCM detects a 

high voltage condition 
on the 1-3-5 shift 
solenoid, 2-4-6-R shift 
solenoid and select 
solenoid voltage feed 
circuit when the 
gearshift control box 
relay is commanded 
OFF.

• Relay power feed 

circuit is open circuit or 
high resistance.

• Relay control circuit is 

short to ground, open 
circuit or high 
resistance.

• Relay voltage feed 

circuit is short to 
battery, open circuit or 
high resistance.

• Poor harness 

connector connection.

• Faulty relay.
• Faulty TCM.

P0902

65

ON

Intermitten

tly ON

Clutch Actuator 
Circuit Low 
Voltage

• The ignition switch 

is ON.

• The ignition voltage 

is more than 20 
volts.

• The emergency 

switch is OFF.

• The smoother main 

relay is commanded 
ON.

• The TCM detects a low 

voltage condition on the 
gearshift clutch 
solenoid valve control 
circuit when the 
solenoid valve is 
commanded ON.

• Solenoid valve control 

circuit is short ground. 

• Poor harness 

connector connection.

• Faulty solenoid valve.
• Faulty TCM.

DTC

Flash 
Code

W/L 

Status

Buzzer 

Status

DTC Name 

Condition for Running 

the DTC

Condition for Setting the 

DTC

Possible Cause