Subaru Legacy IV (2008 year). Service manual - part 994

AC(diag)-28

Diagnostic Procedure for Actuators

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

5

CHECK AIR MIX DOOR ACTUATOR POSI-
TION SWITCH SIGNAL.
1) Connect the connector of auto A/C control 
module and air mix door actuator.
2) Turn the ignition switch and AUTO switch to 
ON.
3) Check the voltage between auto A/C control 
module connector terminals while changing the 
setting temperature between maximum COOL 
and maximum HOT.

Connector & terminal

Driver’s side

(B282) No. 24 (+) — (B282) No. 27 (–):

Passenger’s side

(B282) No. 4 (+) — (B282) No. 27 (–):

Does the voltage change 
between 1 V (Max. HOT) and 4 
V (Max. COOL)?

Go to step 6.

Replace the air mix 
door actuator.

6

CHECK POOR CONTACT.
Check poor contact of auto A/C control module 
and connector.

Is there poor contact in connec-
tor?

Repair the connec-
tor.

Replace the auto 
A/C control mod-
ule.

Step

Check

Yes

No

AC(diag)-29

Diagnostic Procedure for Sensors

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

8. Diagnostic Procedure for Sensors

A: AMBIENT SENSOR

TROUBLE SYMPTOM:
Fan speed is not switched when the fan speed control dial is in AUTO position.
WIRING DIAGRAM:

B282

F78

10

9

B282

2

1

F78

1 2

10

11

14

13

B26

B25

C3

C10

F108

B361

B280

B281

B:

C:

5

4

6 7

8

2

1

9

3

10

22

23

11 12 13 14 15

24 25

26 27

16 17 18

28 29

19 20

21

30

B280

B281

B:

5 6 7

8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26

27 28

16 17 18 19

20 21

C:

1 2 3

4 5 6

7 8 9 10 11 12 13 14

B361

1 2 3

8

9 10

4

11 12 13 14 15 16

5 6 7

17 18

F108

AC-01652

1 2 3 4 5 6 7 8 9 10

21 22 23 24 25 26 27 28 29 30

11 12 13 14 15 16 17 18 19 20
31 32 33 34 35 36 37 38 39 40

AUTO A/C 

CONTROL MODULE

AMBIENT

SENSOR

THROUGH
JOINT CONNECTOR

BODY INTEGRATED UNIT

AC(diag)-30

Diagnostic Procedure for Sensors

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK AMBIENT SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ambient 
sensor.
3) Measure the resistance between connector 
terminals of ambient sensor.

Terminals

No. 1 — No. 2:

Is the resistance approximately 
2.2 k

: at 25°C (77°F) ?

Go to step 2.

Replace the ambi-
ent sensor.

2

CHECK INPUT SIGNAL FOR AMBIENT SEN-
SOR.
1) Turn the ignition to ON.
2) Measure the voltage between connector 
(F78) terminals.

Connector & terminal

(F78) No. 2 (+) — No. 1 (–):

Is the voltage approx. 5 V?

Go to step 6.

Go to step 3.

3

CHECK OUTPUT SIGNAL OF BODY INTE-
GRATED UNIT.
1) Turn the ignition switch to OFF.
2) Draw out the body integrated unit.
3) Disconnect the connector from ambient 
sensor.
4) Turn the ignition switch to ON.
5) Measure the voltage between connector 
terminals of body integrated unit.

Connector & terminal

(B281) No. 3 (+) — No. 10 (–):

Is the voltage approx. 5 V?

Go to step 4.

Go to step 6.

4

CHECK HARNESS CONNECTOR BETWEEN 
BODY INTEGRATED UNIT AND AMBIENT 
SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from body inte-
grated unit.
3) Measure the resistance of harness between 
body integrated unit and ambient sensor.

Connector & terminal

(F78) No. 1 — (B281) No. 10:

Is the resistance less than 1 

:? Go to step 5.

Repair the open 
circuit of harness 
between body inte-
grated unit and 
ambient sensor.

5

CHECK HARNESS CONNECTOR BETWEEN 
BODY INTEGRATED UNIT AND AMBIENT 
SENSOR.
Measure the resistance of harness between 
body integrated unit and ambient sensor.

Connector & terminal

(F78) No. 2 — (B281) No. 3:

Is the resistance less than 1 

:? Go to step 6.

Repair the open 
circuit of harness 
between body inte-
grated unit and 
ambient sensor.

6

CHECK DTC.
1) Connect the connectors of body integrated 
unit and ambient sensor as originally con-
nected.
2) Read the DTC of body integrated unit using 
Subaru Select Monitor.

Is DTC “U xxx” of CAN commu-
nication displayed?

Check the commu-
nication circuit. 
<Ref. to 
LAN(diag)-2, Basic 
Diagnostic Proce-
dure.>

Go to step 7.

7

CHECK POOR CONTACT.
Check poor contact of auto A/C control module 
connector.

Is there poor contact in connec-
tor?

Repair the connec-
tor.

Replace the auto 
A/C control mod-
ule.

AC(diag)-31

Diagnostic Procedure for Sensors

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

B: IN-VEHICLE SENSOR

TROUBLE SYMPTOM:
Blower fan speed, outlet port and inlet port do not change after turning the AUTO switch to ON.
WIRING DIAGRAM:

B282

i55

B282

27

5

2

1

i3

B38

i55

1 2

12

11

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

B38

1 2 3 4 5 6 7 8 9 10

21 22 23 24 25 26 27 28 29 30

11 12 13 14 15 16 17 18 19 20
31 32 33 34 35 36 37 38 39 40

AC-01649

IN-VEHICLE SENSOR

AUTO A/C 
CONTROL MODULE