Isuzu N-Series. Service 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