Subaru Legacy IV (2008 year). Service manual - part 709

4AT(diag)-57

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

O: DTC P0743 TORQUE CONVERTER CLUTCH CIRCUIT ELECTRICAL

DTC DETECTING CONDITION:
Output signal circuit of lock-up duty solenoid is open or shorted.
TROUBLE SYMPTOM:
No lock-up occurs. (After engine is warmed up)
WIRING DIAGRAM:

AT-04768

TCM

B11

1

2

3 4

5

6 7

8

9

13

14 15

20

19

17

16

10

11 12

18

6

B54

B11

AT 2

T4

12

6

B54

5

6

7 8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26 27

28

16

17 18 19 20 21

33 34

29

32

30

31

35

AT2

10

9

8

7

6

5

4

3

2

1

CONTROL VALVE BODY

LOCK-UP
DUTY
SOLENOID

4AT(diag)-58

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK DTC.

Are multiple DTCs displayed?

Go to other DTC.

Go to step 2.

2

CHECK HARNESS CONNECTOR BETWEEN 
TCM AND TRANSMISSION.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from TCM and 
transmission.
3) Measure the resistance of harness between 
TCM connector and transmission connector.

Connector & terminal

(B54) No. 6 — (B11) No. 12:

Is the resistance less than 1 

:? Go to step 3.

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

3

CHECK HARNESS CONNECTOR BETWEEN 
TCM AND TRANSMISSION.
Measure the resistance of the harness connec-
tor between TCM connector and chassis 
ground.

Connector & terminal

(B54) No. 6 — Chassis ground:

Is the resistance 1 M

: or 

more?

Go to step 4.

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

4

CHECK LOCK-UP DUTY SOLENOID.
Measure the resistance between transmission 
connector receptacle’s terminals.

Connector & terminal

(T4) No. 12 — No. 20:

Is the resistance 2.0 — 6.0 

:? Go to step 5.

Go to step 8.

5

CHECK OUTPUT SIGNAL FROM TCM US-
ING SUBARU SELECT MONITOR.
1) Connect the connectors to TCM and trans-
mission.
2) Lift up the vehicle.
3) Connect the Subaru Select Monitor to data 
link connector.
4) Start the engine, and run the Subaru Select 
Monitor.
5) Start the engine and warm up the engine 
until the ATF temperature exceeds 80°C 
(176°F).

NOTE:
If the ambient temperature is below 0°C (32°F),
drive the vehicle until the ATF reaches its oper-
ating temperature.
6) Read the data of “Lock Up Duty Ratio” using 
Subaru Select Monitor.
• Lock-up duty solenoid is indicated in “%”.
7) Shift the select lever to “D”, and slowly 
increase vehicle speed to 60 km/h (37 MPH).

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.>

Is the measured value 95%?

Go to step 6.

Go to step 7.

4AT(diag)-59

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

6

CHECK OUTPUT SIGNAL FROM TCM US-
ING SUBARU SELECT MONITOR.
Return the engine to idling speed, shift the 
select lever to “N” range and read the data.

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.>

Is the measured value 5%?

Even if the ATF 
temperature warn-
ing light blinks, the 
circuit is in normal 
condition at this 
time. A temporary 
poor contact of 
connector or har-
ness may be the 
cause. Repair the 
harness or con-
nector in TCM and 
transmission.

Go to step 7.

7

CHECK POOR CONTACT.

Is there poor contact in lock-up 
duty solenoid circuit?

Repair the poor 
contact.

Replace the TCM. 
<Ref. to 4AT-61, 
Transmission Con-
trol Module 
(TCM).>

8

CHECK LOCK-UP DUTY SOLENOID (IN 
TRANSMISSION).
1) Disconnect the transmission connector.
2) Drain the automatic transmission fluid.

CAUTION:
Do not drain ATF until it cools down.
3) Remove the oil pan, and disconnect the 
connector from control valve body.
4) Measure the resistance between lock-up 
duty solenoid and transmission ground.

Connector & terminal

(AT2) No. 6 — Transmission ground:

Is the resistance 2.0 — 6.0 

:? Go to step 9.

Replace the con-
trol valve body. 
<Ref. to 4AT-56, 
Control Valve 
Body.>

9

CHECK HARNESS CONNECTOR BETWEEN 
LOCK-UP DUTY SOLENOID AND TRANS-
MISSION.
Measure the resistance of harness between 
lock-up duty solenoid and transmission connec-
tor.

Connector & terminal

(T4) No. 12 — (AT2) No. 6:

Is the resistance less than 1 

:? Go to step 10.

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

10

CHECK HARNESS CONNECTOR BETWEEN 
LOCK-UP DUTY SOLENOID AND TRANS-
MISSION.
Measure the resistance of harness between 
transmission connector and transmission 
ground.

Connector & terminal

(T4) No. 12 — Transmission ground:

Is the resistance 1 M

: or 

more?

Even if the ATF 
temperature warn-
ing light blinks, the 
circuit is in normal 
condition at this 
time. A temporary 
poor contact of 
connector or har-
ness may be the 
cause. Repair the 
harness or con-
nector in lock-up 
duty solenoid and 
transmission.

Repair the short 
circuit of harness 
between lock-up 
duty solenoid and 
transmission con-
nector.

Step

Check

Yes

No

4AT(diag)-60

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

P: DTC P0748 PRESSURE CONTROL SOLENOID “A” ELECTRICAL

DTC DETECTING CONDITION:
Output signal circuit of line pressure linear solenoid is open or shorted.
TROUBLE SYMPTOM:
Excessive shift shock
WIRING DIAGRAM:

AT-04769

3

B11

AT2

T4

B11

1

2

3 4

5

6 7

8

9

13

14 15

20

19

17

16

10

11 12

18

4

B54

5

6

7 8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26 27

28

16

17 18 19 20 21

33 34

29

32

30

31

35

10

1

2

5

B54

TCM

CONTROL VALVE BODY

LINE
PRESSURE
LINEAR
SOLENOID

AT2

10

9

8

7

6

5

4

3

2

1