Subaru Legacy IV (2008 year). Manual - part 768

5AT(diag)-87

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

AD:DTC P0958 BACKUP LIGHT RELAY CIRCUIT HIGH

DTC DETECTING CONDITION:
Output circuit of the back-up light relay is open or shorted
TROUBLE SYMPTOM:
Back-up light does not illuminate in “R” range.
WIRING DIAGRAM:

13

B55

B226

TCM

IG2 RELAY

No.1

8

E

1

3

2

4

B226

B55

5

6

7

2

1

3

4

29

10 11 12 13 14 15

25

24

16

30

9

8

17 18 19

20
28

21 22 23

32

31

26 27

33

34 35

10
11

6

5

1

4

2

3

8 9

7

MAIN SBF

SBF-8

B

A

TTER

Y

BACK-UP LIGHT RELAY

BACK-UP LIGHT SYSTEM

AT-04365

5AT(diag)-88

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK DTC OF TCM.

Is DTC of Transmission Range 
Sensor Circuit (PRNDL Input) 
detected?

Perform the diag-
nosis according to 
DTC.

Go to step 2.

2

CHECK HARNESS CONNECTOR BETWEEN 
TCM AND BACK-UP LIGHT RELAY.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from TCM and 
back-up light relay.
3) Measure the resistance of harness between 
TCM connector and back-up light relay connec-
tor.

Connector & terminal

(B55) No. 13 — (B226) No. 4:

Is the resistance less than 1 

:? Go to step 3.

Repair the open 
circuit of harness 
between TCM and 
transmission con-
nector, or poor 
contact of connec-
tor.

3

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

Connector & terminal

(B55) No. 13 — 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 TCM OUTPUT SIGNAL.
1) Turn the ignition switch to ON. (engine OFF)
2) Shift the select lever to “P” range.
3) Measure the voltage between TCM connec-
tor and chassis ground.

Connector & terminal

(B55) No. 13 (+) — Chassis ground (–):

Is the voltage 8 V or more?

Go to step 5.

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

5

CHECK TCM OUTPUT SIGNAL.
1) Set the select lever to “R” range.
2) Measure the voltage between TCM connec-
tor and chassis ground.

Connector & terminal

(B55) No. 13 (+) — Chassis ground (–):

Is the voltage 1 V or less?

Go to step 6.

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

6

CHECK INPUT VOLTAGE FOR BACK-UP 
LIGHT RELAY.
Measure the voltage between back-up light 
relay and chassis ground.

Is the voltage 10 — 13 V?

Replace the back-
up light relay.

Check open or 
short circuit of har-
ness between fuse 
(No. 18) and back-
up light relay.

5AT(diag)-89

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

AE:DTC P1706 AT VEHICLE SPEED SENSOR CIRCUIT MALFUNCTION 

(REAR WHEEL)

DTC DETECTING CONDITION:
Input signal circuit of TCM is open or shorted.
TROUBLE SYMPTOM:
• Shifting quality malfunction
• Tight corner braking phenomenon occurs.
WIRING DIAGRAM:

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. 23 — (B12) No. 5:
(B54) No. 27 — (B11) No. 7:
(B54) No. 16 — (B11) No. 2:

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. 23 — Chassis ground:
(B54) No. 27 — Chassis ground:
(B54) No. 16 — 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.

AT-04366

B54

27

7

AT4

TCM

16

2

B11

23

5

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

AT4

1

3

1

2

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

B11

T4

B12

T3

B12

8

7

6

5

4

3

2

1

2 3

REAR VEHICLE SPEED SENSOR

5AT(diag)-90

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

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

(B12) No. 5 (+) — (B11) No. 2 (–):

Is the voltage 4 — 6 V?

Go to step 7.

Go to step 6.

6

CHECK HARNESS ASSEMBLY (TURBINE 
SPEED SENSOR GROUND).
Check the installing condition of ground con-
necting harness (used for both of turbine speed 
sensor 1, rear vehicle speed sensor).

Is the ground connecting har-
ness installed to transmission 
body correctly, or the harness 
and connector terminals not 
damaged?

Go to step 7.

When the poor 
installation of 
ground connecting 
harness, install it 
securely.
Replace the trans-
mission assembly 
when the harness 
is damaged. <Ref. 
to 5AT-39, Auto-
matic Transmis-
sion Assembly.>

7

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 the vehicle.
4) Read the current data of rear wheel speed 
using Subaru Select Monitor. <Ref. to 
5AT(diag)-18, OPERATION, 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 rear 
wheel speed depending 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 poor con-
tact of harness in 
ATF temperature 
sensor and trans-
mission connector.

Replace the trans-
mission harness.

Step

Check

Yes

No