Subaru Legacy IV (2008 year). Service manual — part 758

5AT(diag)-47

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK DTC.

Is any of following DTC dis-
played? / AT CAN Communica-
tion Circuit / Output Speed
Sensor Circuit / AT Vehicle
Speed Sensor Circuit Malfunc-
tion (Rear Wheel)

Perform the diag-
nosis according to
DTC.

Go to step 2.

2

CHECK FUSE (RELAY BLOCK).
Remove the fuse (7.5A) in the relay block.

Is the fuse (7.5A) blown out?

Replace the fuse
(7.5A). If the
replaced fuse
(7.5A) has blown
out easily, repair
short circuit of har-
ness between fuse
(7.5A) and body
integrated unit.

Go to step 3.

3

CHECK BODY INTEGRATED UNIT.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor to data
link connector.
3) Turn the ignition switch to ON. (engine OFF)
4) Turn the Subaru Select Monitor switch to ON.
5) Depress the brake pedal.
6) Read the data of "Stop Light Switch" using
Subaru Select Monitor. <Ref. to LAN(diag)-12,
OPERATION, Subaru Select Monitor.>

Is ON displayed?

Go to step 4.

Go to step 5.

4

CHECK TCM.
Read the data of "Stop Light Switch" using Sub-
aru Select Monitor. <Ref. to 5AT(diag)-18,
OPERATION, Subaru Select Monitor.>

Is ON displayed?

A temporary poor
contact of connector
or harness may be
the cause. Check
the poor contact.

Replace the TCM.
<Ref. to 5AT-60,
Transmission Con-
trol Module
(TCM).>

5

CHECK BODY INTEGRATED UNIT INPUT
SIGNAL.
1) Disconnect the connector from body inte-
grated unit.
2) Depress the brake pedal.
3) Measure the voltage between body inte-
grated unit connector and chassis ground.

Connector & terminal

(B281) No. 23 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 8.

Go to step 6.

6

CHECK HARNESS CONNECTOR BETWEEN
BODY INTEGRATED UNIT AND STOP LIGHT
SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from stop light
switch.
3) Measure the resistance of harness between
body integrated unit and stop light switch.

Connector & terminal

(B281) No. 23 — (B65) No. 3:

Is the resistance less than 1

:? Go to step 7.

Repair the open
circuit of harness
between body inte-
grated unit and
stop light switch.

7

CHECK HARNESS CONNECTOR BETWEEN
BODY INTEGRATED UNIT AND STOP LIGHT
SWITCH.
Measure the resistance of harness between
body integrated unit connector and stop light
switch.

Connector & terminal

(B281) No. 23 — Chassis ground:

Is the resistance 1 M

: or

more?

Go to step 8.

Repair the short
circuit of harness
between body inte-
grated unit and
stop light switch.

8

CHECK POOR CONTACT.

Is there poor contact in input
signal of brake switch?

Repair the poor
contact.

Check the body
integrated unit.

5AT(diag)-48

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

F: DTC P0720 OUTPUT SPEED SENSOR CIRCUIT

DTC DETECTING CONDITION:
• AT vehicle speed signal is abnormal.
• The harness connector between TCM and front vehicle speed sensor is shorted or open.
TROUBLE SYMPTOM:
• Shifting quality malfunction
• Driving performance is poor.
WIRING DIAGRAM:

AT-04414

T15

1

2

3

B11

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

B54

B11

T4

TCM

16

27

B54

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

7

24

CONTROL
VALVE BODY

T15

FRONT VEHICLE
SPEED SENSOR

2

1

2

T10

3

4

1

T14

2

1 2 3
4 5 6

T14

T10

1 2 3 4
6 7 8 9

5

10

1

5AT(diag)-49

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK TCM I/O SIGNAL.
Check the power supply and ground I/O signals.
<Ref. to 5AT(diag)-14, ELECTRICAL SPECIFI-
CATION, Transmission Control Module (TCM) I/
O Signal.>

Is TCM I/O signal OK?

Go to step 2.

Repair the open or
short circuit for
power supply and
ground.

2

CHECK TCM AND TRANSMISSION HAR-
NESS CONNECTOR.
1) Disconnect the connectors from TCM and
transmission.
2) Measure the resistance of harness between
TCM connector and transmission connector.

Connector & terminal

(B54) No. 24 — (B11) No. 1:
(B54) No. 16 — (B11) No. 2:
(B54) No. 27 — (B11) No. 7:

Is the resistance less than 1

:? Go to step 3.

Repair the open
circuit of harness
between TCM and
transmission con-
nector.

3

CHECK TCM AND TRANSMISSION HAR-
NESS CONNECTOR.
Measure the resistance of harness between
TCM connector and chassis ground.

Connector & terminal

(B54) No. 24 — Chassis ground:

Is the resistance less than 1 M

:? Go to step 4.

Repair the short
circuit of harness
between TCM and
transmission con-
nector.

4

CHECK TCM POWER SUPPLY OUTPUT.
1) Connect the connector to the TCM. (Trans-
mission connector is disconnected)
2) Turn the ignition switch to ON. (engine OFF)
3) Measure the voltage between transmission
connector and chassis ground.

Connector & terminal

(B11) No. 7 (+) — Chassis ground (–):

Is the voltage 10 — 13 V?

Go to step 5.

Replace the TCM.
<Ref. to 5AT-60,
Transmission Con-
trol Module
(TCM).>

5

CHECK INPUT CIRCUIT OF TCM TURBINE
SPEED SENSOR.
Measure the voltage variation between TCM
connector terminals.

Connector & terminal

(B11) No. 1 (+) — (B11) No. 2 (–):

Is the voltage 4 — 6 V?

Go to step 6.

Replace the TCM.
<Ref. to 5AT-60,
Transmission Con-
trol Module
(TCM).>

6

CHECK INPUT SIGNAL FOR TCM USING
SUBARU SELECT MONITOR.
1) Connect all connectors.
2) Lift up the vehicle.

NOTE:
Raise all wheels off the floor.
3) Start the engine, and drive it.
4) Read the current data of front wheel speed
using Subaru Select Monitor. <Ref. to
5AT(diag)-18, READ CURRENT DATA, OPER-
ATION, Subaru Select Monitor.>

NOTE:
The speed difference between front and rear
wheels may illuminate the ABS warning light,
but this does not indicate a malfunction. When
AT control diagnosis is finished, perform the
ABS or VDC clear memory of on-board diag-
nostics system. <Ref. to ABS(diag)-20, Clear
Memory Mode.> <Ref. to VDC(diag)-23, Clear
Memory Mode.>

Does the value of the front
wheel speed change depend-
ing on the acceleration and
deceleration of the vehicle?

Even if the AT OIL
TEMP light blinks,
the system is in
normal condition.
A temporary poor
contact of connec-
tor or harness may
be the cause.
Repair the poor
contact of harness
between ATF tem-
perature sensor
and transmission
connector.

Go to step 7.

5AT(diag)-50

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

7

CHECK HARNESS CONNECTOR BETWEEN
TRANSMISSION AND CONTROL VALVE
BODY.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from transmis-
sion.
3) Remove the transmission connector from
bracket.
4) Lift up the vehicle.

NOTE:
Raise all wheels off the floor.
5) Drain the ATF.

CAUTION:
Do not drain ATF until it cools down.
6) Remove the oil pan, and disconnect the
connector from control valve body connector.
7) Measure the resistance between transmis-
sion connector and control valve body connec-
tor.

Connector & terminal

(T4) No. 1 — (T10) No. 2:

Is the resistance less than 1

:? Go to step 8.

Repair the open
circuit of harness
between control
valve body con-
nector and trans-
mission connector.

8

CHECK HARNESS CONNECTOR BETWEEN
TRANSMISSION AND CONTROL VALVE
BODY.
Measure the resistance between transmission
ground and control valve body connector.

Connector & terminal

(T10) No. 2 — Transmission ground:

Is the resistance 1 M

: or

more?

Go to step 9.

Repair the short
circuit of harness
between transmis-
sion connector and
transmission
ground.

9

CHECK HARNESS CONNECTOR BETWEEN
CONTROL VALVE BODY AND FRONT VEHI-
CLE SPEED SENSOR.
1) Disconnect the connector from front vehicle
speed sensor.
2) Measure the resistance of harness between
control valve body connector and vehicle speed
sensor connector.

Connector & terminal

(T14) No. 4 — (T15) No. 1:
(T10) No. 2 — (T15) No. 2:
(T14) No. 1 — (T15) No. 3:

Is the resistance less than 1

:? Go to step 10.

Replace the con-
trol valve body.
<Ref. to 5AT-57,
Control Valve
Body.>

10

CHECK HARNESS CONNECTOR BETWEEN
CONTROL VALVE BODY AND FRONT VEHI-
CLE SPEED SENSOR.
Measure the resistance of harness between
control valve body connector and transmission
ground.

Connector & terminal

(T10) No. 2 — Transmission ground:

Is the resistance 1 M

: or

more?

Replace the front
vehicle speed sen-
sor.

Replace the con-
trol valve body.
<Ref. to 5AT-57,
Control Valve
Body.>

Step

Check

Yes

No