Subaru Legacy III (2000-2003 year). Manual - part 784

VDC-172

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

AA:DTC 43 AEC COMMUNICATION LINE MALFUNCTION

DIAGNOSIS:
• AEC communication line is broken or short circuited.
TROUBLE SYMPTOM:
• VDC does not operate.
WIRING DIAGRAM:

C8

C7

C2

C8

C7

LH4

RH4

WO

C2

B5

A12

OO

B18

A4

B6

H6

A11

VDC

CONTROL

MODULE

AET

AEB

AEC

5

7

R

21

43

8

6

1

4

L

2

F87

F96

B255

F87

56 57

59 60

62 63

65

82 83

80

27

28

25

26

23

24

21

22

19

20

17

18

15

16

13

14

11

12

9

10

7

8

5

6

3

4

1

2

54

55

52

53

50

51

81

48

49

46

47

44

45

78

79

76

77

75

42

43

40

41

74

72

73

70

71

39

37

38

35

36

69

67

68

66

33

34

61

64

31

32

29

30

58

B135

ENGINE

CONTROL

MODULE

B134

B135

A:

:

B:

:

H6

RH4 WO

B136

C:

: LH4

OO

RH4

B:

: RH4 WO

: LH4 RH4 OO

B134

A:

: H6

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

1 2 3 4

10 11 12

19 20 21

13

5

6

14 15

7

8 9

16 17

18

22

1 2 3

4 5 6

7 8 9 10 11 12 13 14

F96

L

:

F96

R

:

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

VDC00175

C: B136

3

4

1 2

8 9 10 11 12 13 14

15 16 17 18 19 20

21 22 23 24

5 6

7

: 4 CYLINDER ENGINE RHD MODEL

: 4 CYLINDER ENGINE LHD MODEL

RH4

LH4

: 4 CYLINDER ENGINE

: 6 CYLINDER ENGINE

H4

H6

: RHD MODEL

: LHD MODEL

R

L

: WITHOUT OBD MODEL

: WITH OBD MODEL

OO

WO

VDC-173

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

Step

Value

Yes

No

1

CHECK HARNESS/CONNECTOR BETWEEN 
VDCCM AND ECM.
1) Turn ignition switch to OFF.
2) Disconnect connector from VDCCM.
3) Disconnect connector from ECM.
4) Measure resistance between VDCCM con-

nector and ECM.

Connector & terminal

H4 engine RHD without OBD model

(F87) No. 8 — (B136) No. 2:

H4 engine RHD with OBD model

(F87) No. 8 — (B135) No. 18:

H4 engine LHD model

(F87) No. 8 — (B136) No. 2:

H6 engine model

(F87) No. 8 — (B134) No. 11:

Is the measured value less than the speci-
fied value?

0.5 

Ω

Go to step 2.

Repair harness/
connector 
between VDCCM 
and ECM.

2

CHECK GROUND SHORT OF HARNESS.
Measure resistance between VDCCM connec-
tor and chassis ground.

Connector & terminal

(F87) No. 8 — Chassis ground:

Does the measured value exceed the specified 
value?

1 M

Ω

Go to step 3.

Repair harness/
connector 
between VDCCM 
and ECM.

3

CHECK BATTERY SHORT OF HARNESS.
Measure voltage between VDCCM connector 
and chassis ground.

Connector & terminal

(F87) No. 8 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified 
value?

0.5 V

Go to step 4.

Repair harness/
connector 
between VDCCM 
and ECM.

4

CHECK BATTERY SHORT OF HARNESS.
1) Turn ignition switch to ON.
2) Measure voltage between VDCCM connec-

tor and chassis ground.

Connector & terminal

(F87) No. 8 (+) — Chassis ground (

−−−−

):

Is the measured value less than the speci-
fied value?

1 V

Go to step 5.

Repair harness/
connector 
between VDCCM 
and ECM.

5

CHECK HARNESS/CONNECTOR BETWEEN 
VDCCM AND ECM.
1) Turn ignition switch to OFF.
2) Connect connector to ECM.
3) Turn ignition switch to ON.
4) Measure voltage between VDCCM connec-

tor and chassis ground.

Connector & terminal

(F87) No. 8 (+) — Chassis ground (

−−−−

):

Is the measured value within the specified 
range?

10 — 15 V

Go to step 6.

Go to step 9.

6

CHECK POOR CONTACT IN CONNECTORS.
Is there poor contact in connectors between 
ECM and VDCCM?

There is poor contact.

Repair connector.

Go to step 7.

VDC-174

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

7

CHECK VDCCM.
1) Turn ignition switch to OFF.
2) Connect all connectors.
3) Erase the memory.
4) Perform inspection mode.
5) Read out the diagnostic trouble code.

Is the same diagnostic trouble code as in 
the current diagnosis still being output?

Same DTC indicated.

Replace VDCCM.  
<Ref. to VDC-8, 
VDC Control Mod-
ule (VDCCM).>

Go to step 8.

8

CHECK ANY OTHER DIAGNOSTIC TROU-
BLE CODES APPEARANCE.
Are other diagnostic trouble codes being out-
put?

Other DTC indicated.

Proceed with the 
diagnosis corre-
sponding to the 
diagnostic trouble 
code.

A temporary poor 
contact.

9

CHECK ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM connector 

terminal and chassis ground.

Connector & terminal

H4 engine RHD without OBD model

(B136) No. 2 (+) — Chassis ground (

−−−−

):

H4 engine RHD with OBD model

(B135) No. 18 (+) — Chassis ground (

−−−−

):

H4 engine LHD model

(B136) No. 2 (+) — Chassis ground (

−−−−

):

H6 engine model

(B134) No. 11 (+) — Chassis ground (

−−−−

):

Is the measured value within the specified 
range?

10 — 15 V

Repair harness/
connector 
between ECM and 
VDCCM.

Go to step 10.

10

CHECK POOR CONTACT IN CONNECTORS.
Is there poor contact in connector ECM?

There is poor contact.

Repair connector.

Go to step 11.

11

CHECK ENGINE.
Is the engine functioning normally?

Operates properly.

Replace ECM.  
<Ref. to 
FU(H6DO)-46, 
Engine Control 
Module.>

Repair engine.

Step

Value

Yes

No

VDC-175

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

MEMO: