Subaru Legacy (2005 year). Manual - part 626

5AT(diag)-95

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AE:DTC P0957 BACKUP LIGHT RELAY CIRCUIT LOW

DTC DETECTING CONDITION:
Short circuit of back-up light relay output circuit
TROUBLE SYMPTOM:
Back-up light does not illuminate in “R” range.
WIRING DIAGRAM:

AT-03091

11

B55

B356

TCM

B55

B356

MAIN SBF

SBF-8

No.18

E

4

2

3

1

1 2 3 4

10 11 12
19 20 21

13

5 6

14 15

7

8

9

16

17

18

22

23

24

IGNITION
RELAY

BACKUP LIGHT CIRCUIT

BATTERY

1 2

3
4

BACKUP LIGHT
RELAY

5AT(diag)-96

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK DTC OF TCM.

Is DTC of Transmission Range 
Sensor Circuit (PRNDL Input) 
circuit 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 and back-up light relay connec-
tor.

Connector & terminal

(B55) No. 11 — (B356) No. 1:

Is the resistance less than 1 
Ω?

Go to step 3.

Repair the open 
circuit of harness 
between TCM and 
transmission con-
nector, and poor 
contact in 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. 11 — 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 TCM OUTPUT SIGNAL.
1) Turn the ignition switch to ON. (engine 
OFF)
2) Set the select lever to “P” range.

Is the voltage more than 10 V? Go to step 5.

Replace the TCM. 
<Ref. to 5AT-61, 
Transmission Con-
trol Module 
(TCM).>

5

CHECK TCM OUTPUT SIGNAL.
Set the select lever to “R” range.

Is the voltage less than 1 V?

Go to step 6.

Replace the TCM. 
<Ref. to 5AT-61, 
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)-97

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AF:DTC P0958 BACKUP LIGHT RELAY CIRCUIT HIGH

DTC DETECTING CONDITION:
Backup light relay malfunction, or open/short circuit in back-up light relay output circuit
TROUBLE SYMPTOM:
• Back-up light does not illuminate in “R” range.
• Back-up light always illuminate except in “R” range.
WIRING DIAGRAM:

AT-03091

11

B55

B356

TCM

B55

B356

MAIN SBF

SBF-8

No.18

E

4

2

3

1

1 2 3 4

10 11 12
19 20 21

13

5 6

14 15

7

8

9

16

17

18

22

23

24

IGNITION
RELAY

BACKUP LIGHT CIRCUIT

BATTERY

1 2

3
4

BACKUP LIGHT
RELAY

5AT(diag)-98

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

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 and back-up light relay connec-
tor.

Connector & terminal

(B55) No. 11 — (B356) No. 1:

Is the resistance less than 1 
Ω?

Go to step 3.

Repair the open 
circuit of harness 
between TCM and 
transmission con-
nector, and poor 
contact in 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. 11 — 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 TCM OUTPUT SIGNAL.
1) Turn the ignition switch to ON. (engine 
OFF)
2) Set the select lever to “P” range.

Is the voltage more than 10 V? Go to step 5.

Replace the TCM. 
<Ref. to 5AT-61, 
Transmission Con-
trol Module 
(TCM).>

5

CHECK TCM OUTPUT SIGNAL.
Set the select lever to “R” range.

Is the voltage less than 1 V?

Go to step 6.

Replace the TCM. 
<Ref. to 5AT-61, 
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.