Subaru Legacy IV (2008 year). Service manual - part 1017

AB(diag)-56

Diagnostic Chart with Trouble Code

AIRBAG SYSTEM (DIAGNOSTICS)

E: DTC 21 AIRBAG ECM FAILURE

DTC DETECTING CONDITION:
Airbag control module is faulty.

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.

Step

Check

Yes

No

1

CHECK IF DTC 21 IS INDICATED.
Read the DTC. <Ref. to AB(diag)-24, READ 
DIAGNOSTIC TROUBLE CODE (DTC), 
OPERATION, Subaru Select Monitor.>

Does the Subaru Select Moni-
tor display DTC21?

Replace the airbag 
control module. 
<Ref. to AB-20, 
Airbag Control 
Module.>

Perform the Clear 
Memory Mode. 
<Ref. to AB(diag)-
25, CLEAR MEM-
ORY MODE, 
OPERATION, Sub-
aru Select Moni-
tor.>

AB(diag)-57

Diagnostic Chart with Trouble Code

AIRBAG SYSTEM (DIAGNOSTICS)

F: DTC 22 FRONT AIRBAG FIRING OUTPUT

WIRING DIAGRAM:

This DTC is indicated when the front airbag module and the pretensioner are deployed.
Once this DTC is displayed, the memory cannot be cleared. Therefore replace the following parts.
• Airbag control module <Ref. to AB-20, Airbag Control Module.>
• Driver’s airbag module <Ref. to AB-14, Driver’s Airbag Module.>
• Passenger’s airbag module <Ref. to AB-15, Passenger’s Airbag Module.>
• Front sub sensor of both sides <Ref. to AB-21, Front Sub Sensor.>
• Front outer seat belt with pretensioner of both sides <Ref. to SB-18, Front Seat Belt.>
• Steering roll connector <Ref. to AB-25, Roll Connector.>
• Occupant detection system (passenger’s seat cushion & frame assembly) <Ref. to SE-9, Front Seat.>

AB6

AB6

AB18

AB17

AB26

2

1

AB9

AB10

AB21

1

4

2

1

8

7

5

6

3

4

AB2

AB7

AB38

2

1

1

2

1

2

3

4

AB37

3

2

2

1

5

6

4

3

AIRBAG CONTROL MODULE

PRETENSIONER LH

PRETENSIONER RH

STEERING
ROLL 
CONNECTOR

AIRBAG MODULE

(DRIVER SIDE)

AIRBAG MODULE

(PASSENGER SIDE)

AB17

AB18

AB38

1 2

AB26

AB21

AB37

1 2

AB9

AB2

1 2 3 4

AB-02107

18 19 20

21 22 23 24 25 26 27 28

1 2 3 4

11 12 13 14

16 17

15

29 30

18 19 20 21 22 23 24

1 2 3 4

11 12 13 14

16

17

15

18 19 20 21 22 23 24

1 2 3 4

11 12 13 14

16

17

15

10

8

7

6

5

9

10

8

7

6

5

9

10

8

7

6

5

9

AB(diag)-58

Diagnostic Chart with Trouble Code

AIRBAG SYSTEM (DIAGNOSTICS)

G: DTC 26 PASSENGER’S AIRBAG INDICATOR FAILURE

DTC DETECTING CONDITION:
• Passenger’s airbag indicator is faulty.
• Airbag control module is faulty.
• Airbag main harness circuit is open.
• Body harness circuit is open.

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.
WIRING DIAGRAM:

AB6

AB1

B31

7

6

R150

R50

B90

7

8

11

10

PASSENGER'S SEAT  

BELT & AIRBAG  

WARNING LIGHT

17

23

AB6

1 2

3 4

5 6 7 8 9 10

AB1

R50

R150

1 2 3

4 5 6 7

8 9 10

12 13 14 15

11

16

AB-01765

18 19 20

21 22 23 24 25 26 27 28

1 2 3

   5   6   7   8

10

   9

4

11 12 13 14

16 17

15

29 30

1 2 3 4 5 6 7 8

AIRBAG CONTROL MODULE

AB(diag)-59

Diagnostic Chart with Trouble Code

AIRBAG SYSTEM (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK POOR CONTACT.
1) Turn the ignition switch to OFF, disconnect 
the battery ground cable, and wait for 20 sec-
onds or more.
2) Confirm that firm contact is secured for the 
connector between the airbag control module 
and map light.

Is there poor contact in any 
connector?

Replace the airbag 
harness connec-
tor.

Go to step 2.

2

CHECK AIRBAG MAIN HARNESS.
1) Disconnect the connectors (AB6, AB17, 
AB18) from airbag control module.
2) Connect the battery ground terminal and 
turn the ignition switch to ON.

NOTE:
Neither of ON/OFF illuminates when it is nor-
mal.

Does the passenger’s airbag 
indicator illuminate?

Go to step 3.

Go to step 4.

3

CHECK AIRBAG MAIN HARNESS.
1) Turn the ignition switch to OFF.
2) Remove the map light and disconnect the 
connector (R150).
3) Connect the test harness AG connector 
(1AG) to the connectors (AB6, AB17, AB18).
4) Measure the resistance between connector 
(2AG) in the test harness AG and chassis 
ground.

Connector & terminal

(2AG) No. 9 — (2AG) No. 8:
(2AG) No. 9 — Chassis ground:
(2AG) No. 8 — Chassis ground:

Is the resistance 1 M

: or 

more?

Replace the map 
light. <Ref. to LI-
32, REMOVAL, 
Spot Map Light.>

Repair the bulk-
head harness. Or 
replace the airbag 
main harness 
along with body 
harness.

4

CHECK AIRBAG HARNESS.
1) Connect the connectors (7AG) and (8AG) in 
the test harness AG.
2) Connect the battery ground terminal and 
turn the ignition switch to ON.

Does the passenger’s airbag 
indicator illuminate?

Replace the airbag 
control module. 
<Ref. to AB-20, 
Airbag Control 
Module.>

Go to step 5.

5

CHECK AIRBAG HARNESS.
1) Turn the ignition switch to OFF.
2) Connect the test harness AG connector 
(1AG) to the connectors (AB6, AB17, AB18).
3) Measure the resistance between connector 
(2AG) in the test harness AG and connector 
(R150).

Connector & terminal

(2AG) No. 9 — (R150) No. 7:
(2AG) No. 8 — (R150) No. 8:

Is the resistance less than 10 

:? Go to step 6.

Repair the bulk-
head harness. Or 
replace the airbag 
main harness 
along with body 
harness.

6

CHECK BODY HARNESS.
1) Turn the ignition switch to ON.
2) Measure the voltage between connector 
(R150) and chassis ground.

Connector & terminal

(R150) No. 4 — Chassis ground:

Is the voltage 10 V or more?

Replace the map 
light. <Ref. to LI-
32, REMOVAL, 
Spot Map Light.>

Repair the map 
light power supply 
line.