Subaru Legacy IV (2008 year). Manual - part 1044

SB-14

Seat Belt Warning System

SEAT BELT SYSTEM

4. Seat Belt Warning System

A: WIRING DIAGRAM

<Ref. to WI-125, WIRING DIAGRAM, Seat Belt Warning System.>

B: INSPECTION

CAUTION:
• Before diagnosing the airbag system, be sure to turn the ignition switch to OFF, disconnect the
ground cable from the battery, and wait 20 seconds or more before starting to work.
• When replacing the airbag module, seat belt pretensioner, roll connector, control module and sen-
sor, reconnect each part and check that the warning light operates properly.
• When inspecting the airbag main harness, disconnect the airbag module connectors of the driver’s
and passenger’s seats for safety.
• When inspecting the airbag rear harness, disconnect the side airbag module connector, curtain
airbag module connector and seat belt pretensioner connector for safety reasons.
TROUBLE SYMPTOM:
• Driver’s side seat belt warning light does not turn on or off.
• Warning buzzer does not beep.

Step

Check

Yes

No

1

CHECK CURRENT SETTINGS.
1) Prepare the Subaru Select Monitor.
2) Turn the ignition switch to ON (engine OFF) 
and run the “PC application for Subaru Select 
Monitor”.
3) Select “Current Data Display” and read the 
data of “Belt Warning Switch”.

Is the belt warning display ON? Go to step 2.

Turn the belt warn-
ing ON with unit 
customization.

2

CHECK CURRENT DATA.
1) Select “Current Data Display” and read the 
data of “IG power supply voltage”.
2) Turn the ignition switch ON 

mo OFF.

Does the voltage change 
between 10 V or higher 

mo

less than 1.5 V, matching the 
ignition switch ON 

mo OFF 

operation?

Go to step 3.

Check the ignition 
switch circuit.

3

CHECK FUNCTION.
1) Sit in the driver’s seat and passenger’s seat, 
and disconnect the seat belts of both seats.
2) Turn the ignition switch to ON (engine OFF).
3) Check the illumination of the driver’s seat 
belt warning light and map light in the combina-
tion meter and the passenger’s seat belt warn-
ing light in the clock unit, and the sounding of 
the buzzer.

Do the driver’s and passenger’s 
warning lights flash, and does 
the buzzer sound while the 
warning lights are flashing?

Go to step 4.

• Malfunction of 
the driver’s seat 
belt warning light 
oGo to step 10.
• Malfunction of 
the passenger’s 
seat belt warning 
light 

oGo to step 

16.
• The buzzer does 
not sound. 

o Go to 

step 6.

4

CHECK FUNCTION.
1) Wait until the buzzer sound stops in step 3. 
(Approximately 6 seconds from starting to 
sound)
2) Fasten and detach the driver’s and passen-
ger’s seat belts.
3) Check the illumination of the driver’s seat 
belt warning light and map light in the combina-
tion meter and the passenger’s seat belt warn-
ing light in the clock unit, and the sounding of 
the buzzer.

Do each seat belt warning light 
illuminate 

mo turn off accord-

ing to the action?

Go to step 5.

• Malfunction of 
the driver’s seat 
belt warning light 
oGo to step 6.
• Malfunction of 
the passenger’s 
seat belt warning 
light 

oGo to step 

12.

SB-15

Seat Belt Warning System

SEAT BELT SYSTEM

5

CHECK FUNCTION.
1) Wait until the buzzer sound stops in step 3. 
(Approximately 6 seconds from starting to 
sound)
2) Start the engine, and set the vehicle speed 
to 15 km/h (9 MPH) or faster.
3) Check the driver’s and passenger’s seat belt 
warning lights, and sounding of the alarm 
buzzer.

Do the driver’s and passenger’s 
warning lights flash, and does 
the buzzer sound while the 
warning lights are flashing?

The seat belt warn-
ing system is nor-
mal.

Go to step 19.

6

CHECK CURRENT DATA.
1) Select “Current Data Display” and read the 
data of the driver’s seat belt switch.
2) Connect and disconnect the seat belt 
buckle.

Does the seat belt SW display 
turn ON 

mo OFF according to 

the operation?

Go to step 10.

Go to step 7.

7

CHECK HARNESS.
1) Disconnect the negative terminal from the 
battery, and wait for 20 seconds or more.
2) Disconnect the connectors of the body inte-
grated unit and the seat belt buckle switch.
3) Check for a short circuit to battery, open cir-
cuit or short circuit to ground between the body 
integrated unit and the seat belt buckle switch 
LH.

Connector & terminal

(B281) No. 16 — (R108) No. 3:

Is the harness normal?

Go to step 8.

Repair or replace 
the harness.

8

CHECK HARNESS.
Measure the resistance between the seat belt 
buckle switch LH and chassis ground.

Connector & terminal

(R108) No. 1 — Chassis ground:

Is the resistance less than 10 

:? Go to step 9.

Repair or replace 
the harness.

9

CHECK SEAT BELT BUCKLE SWITCH LH.
Measure the resistance between the connector 
terminals of the driver’s seat belt switch when 
the driver’s seat belt is fastened and detached.

Connector & terminal

(R108) No. 1 — (R108) No. 3:

Is the resistance when the belt 
is fastened 1 M

: or more, and 

less then 10 

: when the belt is 

detached?

Replace the body 
integrated unit. 
<Ref. to SL-56, 
REMOVAL, Body 
Integrated Unit.>

Replace the inner 
belt assembly LH. 
<Ref. to SB-18, 
INNER SEAT BELT 
ASSEMBLY, 
REMOVAL, Front 
Seat Belt.>

10

CHECK DTC.
Read the DTC using the Subaru Select Monitor.

Are any body CAN related DTC 
detected?

Check the CAN 
according to DTC.

Go to step 11.

11

CHECK COMBINATION METER.
Perform the self-diagnosis of combination 
meter. <Ref. to IDI-5, SELF-DIAGNOSIS, 
INSPECTION, Combination Meter System.>

At the start of combination 
meter self diagnosis, did the 
buzzer sound and the seat belt 
warning light illuminate?

Replace the body 
integrated unit or 
the combination 
meter. Or, replace 
both. There may 
be a communica-
tion malfunction of 
the body integrated 
unit, or a reception 
malfunction of the 
combination meter.

Replace the com-
bination meter. 
<Ref. to IDI-22, 
REMOVAL, Com-
bination Meter.>

12

CHECK CURRENT DATA.
1) Sit on the passenger’s seat.
2) Select “Current Data Display” and display 
the data of “P seatbelt SW input ”.
3) Fasten and detach the passenger’s side 
seat belt buckle, and read the data of the seat 
belt switch. <Ref. to LAN(diag)-29, OPERA-
TION, Read Current Data.>

Does the seat belt switch dis-
play turn ON 

mo OFF accord-

ing to the operation of the seat 
belt buckle?

Go to step 16.

Go to step 13.

Step

Check

Yes

No

SB-16

Seat Belt Warning System

SEAT BELT SYSTEM

13

CHECK AIRBAG SYSTEM AND OCCUPANT 
DETECTION SYSTEM.
Perform the check in accordance with the diag-
nostic procedure DTC 27 of the airbag system. 
<Ref. to AB(diag)-60, DTC 27 ODS COMMUNI-
CATION ERROR, Diagnostic Chart with Trouble 
Code.>

Is there any problem on the 
inspection result?

Go to step 14.

Repair or replace 
the harness.

14

CHECK BUCKLE SWITCH RH.
Perform the check in accordance with the diag-
nostic procedure DTC 37 of the occupant 
detection system. <Ref. to OD(diag)-27, DTC 
37 BUCKLE SWITCH RH FAILURE, Diagnostic 
Procedure with Diagnostic Trouble Code 
(DTC).>

Is there any problem on the 
inspection result?

Go to step 15.

Repair or replace 
the harness.

15

CHECK AIRBAG CONTROL MODULE AND 
BODY INTEGRATED UNIT.
Check the airbag control module, occupant 
detection sensor and seat belt buckle switch 
RH.
Perform the check in accordance with the diag-
nostic procedure DTC 39 of the airbag system. 
<Ref. to AB(diag)-62, DTC 39 SEAT BELT 
WARNING FAILURE, Diagnostic Chart with 
Trouble Code.>

Is there any problem on the 
inspection result?

Replace the body 
integrated unit. 
<Ref. to SL-56, 
REMOVAL, Body 
Integrated Unit.>

Repair or replace 
the harness.

16

CHECK HARNESS.
1) Disconnect the connector of map light.
2) Turn the ignition switch to ON.
3) Measure the voltage between the body inte-
grated unit and map light.

Connector & terminal

(R150) No. 8 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 17.

Repair or replace 
the harness.

17

CHECK HARNESS.
1) Turn the ignition switch to ON.
2) Disconnect the connector of body inte-
grated unit.
3) Check for short circuit to battery, open cir-
cuit and short circuit to ground between the 
body integrated unit and the map light.

Connector & terminal

(B280) No. 27 — (R150) No. 5:

Is the harness normal?

Go to step 19.

Repair or replace 
the harness.

18

CHECK MAP LIGHT.
1) Connect the map light.
2) Turn the ignition switch to ON.
3) Use an appropriate wiring harness to create 
a short between the body integrated unit and 
the map light.

Connector & terminal

(R150) No. 5 — Chassis ground:

Does passenger’s seat belt 
warning light in the map light 
illuminate?

Replace the body 
integrated unit. 
<Ref. to SL-56, 
REMOVAL, Body 
Integrated Unit.>

Replace the map 
light. <Ref. to IDI-
28, REMOVAL, 
Clock.>

19

CHECK DTC.
Read the DTCs for all systems using the Sub-
aru Select Monitor.

Is a DTC detected?

Perform a check 
according to the 
DTC.

Go to step 20.

Step

Check

Yes

No

SB-17

Seat Belt Warning System

SEAT BELT SYSTEM

20

CHECK CURRENT DATA.
Select “Current Data Display” and read the data 
of the “Front Wheel Speed”. <Ref. to LAN(diag)-
29, OPERATION, Read Current Data.>

Does the data indicate the nor-
mal vehicle speed?

Go to step 11.

Check the follow-
ing items.
• LAN system
<Ref. to 
LAN(diag)-65, 
DTC U1223 CAN-
HS VDC/ABS NO-
RECEIVE DATA, 
Diagnostic Proce-
dure with Diagnos-
tic Trouble Code 
(DTC).>
• Check VDC or 
ABS.

• VDC <Ref. to 
VDC(diag)-2, 
Basic Diagnos-
tic Procedure.>
• ABS <Ref. to 
ABS(diag)-2,
Basic Diagnos-
tic Procedure.>

Step

Check

Yes

No