Subaru Legacy (2005 year). Manual - part 557

4AT(diag)-65

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

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 and transmission connector.

Connector & terminal

(B55) No. 5 — (B11) No. 12:

Is the resistance less than 1 
Ω?

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 harness connector 
between TCM connector and chassis ground.

Connector & terminal

(B55) No. 5 — Chassis ground:

Is the resistance more than 1 
M

Ω?

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 

Ω? Go to step 5.

Go to step 8.

5

CHECK OUTPUT SIGNAL EMITTED FROM 
TCM USING SUBARU SELECT MONITOR.
1) Connect the connectors to TCM and trans-
mission.
2) Lift-up the vehicle.

NOTE:

Raise all wheels off floor.

3) Connect the Subaru Select Monitor to data 
link connector.
4) Start the engine, and turn the Subaru 
Select Monitor power switch to ON.
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 solenoid 
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 light the ABS warning light or VDC
warning light, but this indicates no malfunction.
When AT control diagnosis is finished, perform
the ABS memory clearance procedure or VDC
memory clearance procedure of on-board diag-
nostics system. <Ref. to ABS(diag)-26, Clear
Memory Mode.> <Ref. to VDC(diag)-25, Clear
Memory Mode.>

Is the value 95%?

Go to step 6.

Go to step 7.

Step

Check

Yes

No

4AT(diag)-66

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

CHECK OUTPUT SIGNAL EMITTED FROM 
TCM USING 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 light the ABS warning light or VDC
warning light, but this indicates no malfunction.
When AT control diagnosis is finished, perform
the ABS memory clearance procedure or VDC
memory clearance procedure of on-board diag-
nostics system. <Ref. to ABS(diag)-26, Clear
Memory Mode.> <Ref. to VDC(diag)-25, Clear
Memory Mode.>

Is the value 5%?

Even if the SPORT 
indicator light is 
blinking, the cir-
cuit has returned 
to normal condi-
tion at this time. A 
temporary poor 
contact of connec-
tor or harness may 
be the cause. 
Repair the har-
ness or connector 
in TCM and trans-
mission.

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-66, 
Transmission Con-
trol Module 
(TCM).>

8

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

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

(AT3) No. 4 — Transmission ground:

Is the resistance 2.0 — 6.0 

Ω? Go to step 9.

Replace the con-
trol valve body. 
<Ref. to 4AT-62, 
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 con-
nector.

Connector & terminal

(T4) No. 12 — (AT3) No. 4:

Is the resistance less than 1 
Ω?

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 more than 1 
M

Ω?

Even if the SPORT 
indicator light is 
blinking, the cir-
cuit has returned 
to normal condi-
tion at this time. A 
temporary poor 
contact of connec-
tor or harness may 
be the cause. 
Repair the har-
ness or connector 
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)-67

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

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:

Step

Check

Yes

No

1

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

Connector & terminal

(B55) No. 19 — (B11) No. 2:
(B55) No. 20 — (B11) No. 1:

Is the resistance less than 1 
Ω?

Go to step 2.

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

2

CHECK HARNESS CONNECTOR BETWEEN 
TCM AND CHASSIS GROUND.
Measure the resistance of harness between 
TCM connector and chassis ground.

Connector & terminal

(B55) No. 19 — Chassis ground:
(B55) No. 20 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 3.

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

3

CHECK LINE PRESSURE LINEAR SOLE-
NOID.
Measure the resistance between transmission 
connector receptacle’s terminals.

Connector & terminal

(T4) No. 1 — No. 2:

Is the resistance 4 — 8 

Ω?

Repair the TCM. 
<Ref. to 4AT-66, 
Transmission Con-
trol Module 
(TCM).>

Go to step 4.

AT-01486

19

B55

B11

AT2

T4

TCM

B11

1

2

3 4

5

6 7

8

9

13

14 15

20

19

17

16

10

11 12

18

42

20

21

B55

AT2

1

2

7

8

9

5

6

3

4

10 11 12

19 20 21

29 30 31

13 14 15 16 17

27 28

18

22 23 24 25 26

3 4

1 2

TRANSMISSION

LINE 
PRESSURE 
LINEAR 
SOLENOID

4AT(diag)-68

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

4

CHECK LINE PRESSURE LINEAR SOLE-
NOID (IN TRANSMISSION).
1) Remove the transmission connector from 
bracket.
2) Drain the ATF.

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 line pres-
sure linear solenoid connector terminals.

Connector & terminal

(AT2) No. 2 — No. 4:

Is the resistance 4 — 8 

Ω?

Go to step 5.

Replace the con-
trol valve body. 
<Ref. to 4AT-62, 
Control Valve 
Body.>

5

CHECK HARNESS CONNECTOR BETWEEN 
TRANSMISSION AND LINE PRESSURE LIN-
EAR SOLENOID.
Measure the resistance of harness between 
line pressure linear solenoid and transmission 
connector.

Connector & terminal

(T4) No. 2 — (AT2) No. 4:
(T4) No. 1 — (AT2) No. 2:

Is the resistance less than 1 
Ω?

Go to step 6.

Repair the open 
circuit of harness 
between line pres-
sure linear sole-
noid and 
transmission con-
nector.

6

CHECK HARNESS CONNECTOR BETWEEN 
TRANSMISSION AND LINE PRESSURE LIN-
EAR SOLENOID.
Measure the resistance of harness between 
transmission connector and transmission 
ground.

Connector & terminal

(T4) No. 1 — Transmission ground:
(T4) No. 2 — Transmission ground:

Is the resistance more than 1 
M

Ω?

Even if the SPORT 
indicator light is 
blinking, the cir-
cuit has returned 
to normal condi-
tion at this time. A 
temporary poor 
contact of connec-
tor or harness may 
be the cause. 
Repair the har-
ness or connector 
in line pressure lin-
ear solenoid and 
transmission.

Repair the short 
circuit of harness 
between line pres-
sure linear sole-
noid and 
transmission con-
nector.

Step

Check

Yes

No