Subaru Legacy (2005 year). Service manual - part 796

VDC(diag)-49

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK POOR CONTACT IN CONNECTOR.
Check if there is poor contact between 
VDCCM&H/U and ABS wheel speed sensor.

Is there poor contact?

Repair the con-
nector.

Go to step 2.

2

CHECK HARNESS CONNECTOR BETWEEN 
VDCCM&H/U AND ABS WHEEL SPEED 
SENSOR.
1) Disconnect the connector (B310) from 
VDCCM&H/U.
2) Disconnect the connector from ABS wheel 
speed sensor.
3) Measure the resistance between 
VDCCM&H/U connector and ABS wheel 
speed sensor connector.

Connector & terminal
DTC C0021

(B310) No. 22 — (B6) No. 1:
(B310) No. 21 — (B6) No. 2:

DTC C0023

(B310) No. 41 — (B15) No. 1:
(B310) No. 25 — (B15) No. 2:

DTC C0025

(B310) No. 23 — (R72) No. 1:
(B310) No. 38 — (R72) No. 2:

DTC C0027

(B310) No. 24 — (R73) No. 1:
(B310) No. 40 — (R73) No. 2:

Is the resistance less than 0.5 
Ω?

Go to step 3.

Repair the har-
ness connector 
between 
VDCCM&H/U and 
ABS wheel speed 
sensor.

3

CHECK GROUND SHORT OF HARNESS.
Measure the resistance between VDCCM&H/U 
connector and chassis ground.

Connector & terminal
DTC C0021

(B310) No. 21 — Chassis ground:

DTC C0023

(B310) No. 25 — Chassis ground:

DTC C0025

(B310) No. 38 — Chassis ground:

DTC C0027

(B310) No. 40 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 4.

Repair the har-
ness connector 
between 
VDCCM&H/U and 
ABS wheel speed 
sensor.

4

CHECK ABS WHEEL SPEED SENSOR POW-
ER SUPPLY CIRCUIT.
1) Connect the VDCCM&H/U connector.
2) Turn the ignition switch to ON.
3) Measure the voltage between ABS wheel 
speed sensor connector and chassis ground.

Connector & terminal
DTC C0021

(B6) No. 1 (+) — Chassis ground (

−

):

DTC C0023

(B15) No. 1 (+) — Chassis ground (

−

):

DTC C0025

(R72) No. 1 (+) — Chassis ground (

−

):

DTC C0027

(R73) No. 1 (+) — Chassis ground (

−

):

Is the voltage 5 — 16 V?

Go to step 6.

Go to step 5.

VDC(diag)-50

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

5

CHECK VDCCM&H/U POWER SUPPLY CIR-
CUIT.
1) Turn the ignition switch to OFF.
2) Disconnect the VDCCM&H/U connector.
3) Turn the ignition switch to ON.
4) Measure the voltage between VDCCM&H/
U connector terminals.

Connector & terminal

(B310) No. 14 (+) — (B310) No. 6 (

−

):

Is the voltage 10 — 15 V?

Go to step 8.

Check the genera-
tor, battery and 
VDCCM&H/U 
power supply cir-
cuit.

6

CHECK ABS WHEEL SPEED SENSOR SIG-
NAL.
1) Install the ABS wheel speed sensor.
2) Prepare an oscilloscope.
3) Check the ABS wheel speed sensor. <Ref. 
to ABS-15, ABS WHEEL SPEED SENSOR, 
INSPECTION, Rear ABS Wheel Speed Sen-
sor.>

Does the oscilloscope indicate 
the waveform pattern like 
shown in the figure when the 
tire is slowly turned? Does the 
oscilloscope indication repeat 
the waveform pattern like 
shown in the figure when the 
tire is slowly turned in equal 
speed for more one rotation?

Go to step 8.

Go to step 7.

7

CHECK ABS WHEEL SPEED SENSOR OR 
MAGNETIC ENCODER.

Are there foreign materials, 
breakage or damage in the 
protrusion of ABS wheel speed 
sensor or magnetic encoder?

Remove dirt 
throughly. Also 
replace the ABS 
wheel speed sen-
sor or magnetic 
encoder as a unit 
with hub unit bear-
ing if it is broken or 
damaged.

Go to step 8.

8

CHECK VDCCM&H/U.
1) Connect all the connectors.
2) Perform the clear memory mode.
3) Perform the inspection mode. <Ref. to 
VDC(diag)-24, PROCEDURE, Inspection 
Mode.>
4) Read the DTC.

Is the same DTC displayed?

Replace the 
VDCCM&H/U. 
<Ref. to VDC-7, 
VDC Control Mod-
ule and Hydraulic 
Control Unit 
(VDCCM&H/U).>

Go to step 9.

9

CHECK OTHER DTC DETECTION.

Is any other DTC displayed?

Perform the diag-
nosis according to 
DTC. 

It results from a 
temporary noise 
interference.

Step

Check

Yes

No

VDC(diag)-51

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

I:

DTC C0022 FRONT ABS WHEEL SPEED SENSOR RH SIGNAL MALFUNC-
TION

NOTE:
For the diagnostic procedure, refer to DTC C0028 “REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION”. <Ref. to VDC(diag)-51, DTC C0028 REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

J: DTC C0024 FRONT ABS WHEEL SPEED SENSOR LH SIGNAL MALFUNC-

TION

NOTE:
For the diagnostic procedure, refer to DTC C0028 “REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION”. <Ref. to VDC(diag)-51, DTC C0028 REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

K: DTC C0026 REAR ABS WHEEL SPEED SENSOR RH SIGNAL MALFUNC-

TION

NOTE:
For the diagnostic procedure, refer to DTC C0028 “REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION”. <Ref. to VDC(diag)-51, DTC C0028 REAR ABS WHEEL SPEED SENSOR LH SIGNAL MAL-
FUNCTION, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

L: DTC C0028 REAR ABS WHEEL SPEED SENSOR LH SIGNAL MALFUNC-

TION

DTC DETECTING CONDITION:
• Defective ABS wheel speed sensor signal (noise, irregular signal, etc.)
• Defective harness connector
TROUBLE SYMPTOM:
• ABS does not operate.
• VDC does not operate.

VDC(diag)-52

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

WIRING DIAGRAM:
• LHD model

B15

B6

R73

R72

B310

B98

1 2 3 4

11 12 13 14
27 28 29 30

15 16 17 18
31 32 33 34

19 20 21 22
35 36 37 38

23 24 25 26
39 40 41 42

5

6

7

8

9

10

VDC00299

38

23

25

41

40

24

6

B98

R72

R2

E

1

2

15

14

6

5

R73

1

2

1

2

1

2

B6

B15

21

22

B310

VDCCM & H/U

TWISTED WIRE

FRONT ABS

WHEEL SPEED

SENSOR LH

TWISTED WIRE

TWISTED WIRE

TWISTED WIRE

FRONT ABS

WHEEL SPEED

SENSOR RH

REAR ABS

WHEEL SPEED

SENSOR LH

REAR ABS

WHEEL SPEED

SENSOR RH

1 2

1 2 3

4 5 6 7

8 9 10 11 12 13 14 15 16