Subaru Legacy III (2000-2003 year). Service manual — part 809

VDC-272

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

BG:DTC 74 DIFFERENTIAL PRESSURE OF PRESSURE SENSOR IS TOO BIG.

DIAGNOSIS:
• Faulty pressure sensor
TROUBLE SYMPTOM:
• ABS does not operate.
• VDC does not operate.
WIRING DIAGRAM:

VDC00181

78

36

77

76

F91

VDC5

F88

2
3

F88

F91

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

VDC HYDRAULIC

UNIT

PRIMAR

Y

PRESSURE SENSOR

SECOND

AR

Y

PRESSURE SENSOR

15

13

16

14

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

F87

VDC

CONTROL

MODULE

1

3

4 5 6

2

VDC-273

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

Step

Value

Yes

No

1

CHECK GROUND SHORT OF HARNESS.
1) Turn ignition switch to OFF.
2) Disconnect connector from VDCCM.
3) Disconnect connector (F91) from VDCH/U.
4) Measure resistance between VDCH/U con-

nector and chassis ground.

Connector & terminal

(F91) No. 13 — Chassis ground:
(F91) No. 14 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 2.

Repair harness
between VDCH/U
and VDCCM.

2

CHECK BATTERY SHORT OF HARNESS.
Measure voltage between VDCH/U connector
and chassis ground.

Connector & terminal

(F91) No. 13 (+) — Chassis ground (

−−−−

):

(F91) No. 14 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified
value?

0.5 V

Go to step 3.

Repair harness
between VDCH/U
and VDCCM.

3

CHECK BATTERY SHORT OF HARNESS.
1) Turn ignition switch to ON.
2) Measure voltage between VDCH/U con-

nector and chassis ground.

Connector & terminal

(F91) No. 13 (+) — Chassis ground (

−−−−

):

(F91) No. 14 (+) — Chassis ground (

−−−−

):

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

0.5 V

Go to step 4.

Repair harness
between VDCH/U
and VDCCM.

4

CHECK INPUT VOLTAGE OF PRESSURE
SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from VDCCM.
3) Remove cover from VDCCM. <Ref. to

VDC-19, REMOVE, VDCCM Connector
Cover.>

4) Connect connector to VDCCM.
5) Connect all connectors.
6) Turn ignition switch to ON.
7) Do not depress brake pedal.
8) Measure voltage between VDCCM connec-

tor terminals.

Connector & terminal

(F87) No. 77 (+) — No. 76 (

−−−−

):

(F87) No. 36 (+) — No. 76 (

−−−−

):

Is the measured value within the specified
range?

0.48 — 0.72 V

Go to step 5.

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

5

CHECK BRAKE FLUID LEAKAGE.
Inspect fluid leakage between brake master
cylinder and VDCH/U.
Does brake fluid leak?

Fluid leaks.

Retighten or
replace.

Go to step 6.

6

CHECK BRAKE MASTER CYLINDER.
Inspect brake master cylinder hydraulic pres-
sure. <Ref. to BR-36, OPERATION CHECK
(WITH GAUGES), INSPECTION, Brake
Booster.>
Is hydraulic pressure normal?

Normal.

Go to step 7.

Replace master
cylinder.

VDC-274

VDC (DIAGNOSTICS)

DIAGNOSTICS CHART WITH SELECT MONITOR

7

CHECK BRAKE PEDAL STROKE.
Measure the stroke between non-forced pedal
position and forced pedal position with 50 kg
(110 lb).
Is the measured value less than the specified
value?

95 mm (3.74 in)

Go to step 8.

Perform bleeding
from brake sys-
tem.

8

CHECK INPUT VOLTAGE OF PRESSURE
SENSOR.
1) Depress the brake pedal with 50 kg (110

lb).

2) Measure voltage between VDCCM connec-

tor terminals.

Connector & terminal

A (F87) No. 77 (+) — No. 76 (

−−−−

):

B (F87) No. 36 (+) — No. 76 (

−−−−

):

Does the voltage difference between A and
B exceed the specified value?

0.2 V

Go to step 9.

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

9

CHECK POOR CONTACT IN CONNECTORS.
Is there poor contact in connector between
VDCCM and pressure sensor?

There is poor contact.

Repair connector.

Go to step 10.

10

CHECK VDCCM.
1) Connect all connectors.
2) Erase the memory.
3) Perform inspection mode.
4) 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 11.

11

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.

Step

Value

Yes

No

VDC-275

VDC (DIAGNOSTICS)

GENERAL DIAGNOSTIC TABLE

15.General Diagnostic Table

A: INSPECTION

Symptom

Primary probable cause

Secondary probable cause

Poor braking
effectiveness

Long braking
distance

VDCH/U
VDCCM
Brake pads
Air in brake line
Tire specifications, wear and pressures
Incorrect wiring or piping

Faulty ABS sensor or sensor gap
Faulty steering angle sensor or improper neutral
position
Faulty yaw rate and lateral G sensor or improper
installation
Proportioning valve
Master cylinder
Brake caliper
Disc rotor
Brake pipe
Brake booster

Wheel locks

VDCH/U
VDCCM
Faulty ABS sensor or sensor gap
Incorrect wiring or piping

Faulty steering angle sensor or improper neutral
position
Faulty yaw rate and lateral G sensor or improper
installation
Proportioning valve
Brake caliper
Brake pipe

Brake dragging

VDCH/U
VDCCM
Faulty ABS sensor or sensor gap
Master cylinder
Brake caliper
Parking brake
Axle & wheels
Brake pedal play

Faulty steering angle sensor or improper neutral
position
Faulty yaw rate and lateral G sensor or improper
installation
Brake pads
Brake pipe

Long brake
pedal stroke

Air in brake line
Brake pedal play

VDCH/U
Proportioning valve
Master cylinder
Brake caliper
Brake pads
Brake pipe
Brake booster

Vehicle pitching

VDCH/U
VDCCM
Uneven road
Suspension play or fatigue (reduced
damping)
Incorrect wiring or piping

Faulty ABS sensor or sensor gap
Faulty steering angle sensor or improper neutral
position
Faulty yaw rate and lateral G sensor or improper
installation

Unstable or
uneven braking

VDCH/U
VDCCM
Faulty ABS sensor or sensor gap
Brake caliper
Brake pads
Uneven road
Tire specifications, wear and pressures
Incorrect wiring or piping

Faulty ABS sensor or sensor gap
Faulty steering angle sensor or improper neutral
position
Faulty yaw rate and lateral G sensor or improper
installation
Master cylinder
Disc rotor
Brake pipe
Axle & wheels
Crowned road or banked road
Suspension play or fatigue (reduced damping)