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
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
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
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
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.
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.
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)
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
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.
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).>
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)
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