Subaru Legacy IV (2008 year). Service manual - part 931

VDC(diag)-39

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

12.Diagnostic Procedure with Diagnostic Trouble Code (DTC)

A: DTC C0021 FRONT RIGHT ABS SENSOR CIRCUIT OPEN OR SHORT

NOTE:
For the diagnostic procedure, refer to DTC C0027 “RL WHEEL SPEED SENSOR CIRCUIT OPEN/HIGH IN-
PUT”. <Ref. to VDC(diag)-40, DTC C0027 REAR LEFT ABS SENSOR CIRCUIT OPEN OR SHORT, Diag-
nostic Procedure with Diagnostic Trouble Code (DTC).>

B: DTC C0023 FRONT LEFT ABS SENSOR CIRCUIT OPEN OR SHORT

NOTE:
For the diagnostic procedure, refer to DTC C0027 “RL WHEEL SPEED SENSOR CIRCUIT OPEN/HIGH IN-
PUT”. <Ref. to VDC(diag)-40, DTC C0027 REAR LEFT ABS SENSOR CIRCUIT OPEN OR SHORT, Diag-
nostic Procedure with Diagnostic Trouble Code (DTC).>

C: DTC C0025 REAR RIGHT ABS SENSOR CIRCUIT OPEN OR SHORT

NOTE:
For the diagnostic procedure, refer to DTC C0027 “RL WHEEL SPEED SENSOR CIRCUIT OPEN/HIGH IN-
PUT”. <Ref. to VDC(diag)-40, DTC C0027 REAR LEFT ABS SENSOR CIRCUIT OPEN OR SHORT, Diag-
nostic Procedure with Diagnostic Trouble Code (DTC).>

VDC(diag)-40

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

D: DTC C0027 REAR LEFT ABS SENSOR CIRCUIT OPEN OR SHORT

DTC DETECTING CONDITION:
• Defective ABS wheel speed sensor (broken wire, input voltage too high)
• Defective harness connector
TROUBLE SYMPTOM:
• ABS does not operate.
• VDC does not operate.
WIRING DIAGRAM:

4

3

1

26

27

2

25

B98

R72

R2

E

1

2

15

14

6

5

R73

1

2

B6

B15

R73

R72

1

2

1 2

2 1

6

5

B310

2

1

B15

B6

VDCCM & H/U

B310

4 5 6 7 8 9

26 27 28 29 30

2 3

1

31 32 33 34 35 36

10 11

14 15 16 17 18 19

37 38 39 40

12 13

41 42 43 44 45 46

20 21

23

24

22

25

VDC00501

B98

1 2 3

4 5 6 7

8 9 10 11 12 13 14 15 16

TWISTED P

AIR LINE

TWISTED P

AIR LINE

TWISTED P

AIR LINE

TWISTED P

AIR LINE

TWISTED P

AIR LINE

TWISTED P

AIR LINE

FRONT ABS 

WHEEL SPEED 

SENSOR LH

FRONT ABS 

WHEEL SPEED 

SENSOR RH

REAR ABS 

WHEEL SPEED 

SENSOR LH

REAR ABS 

WHEEL SPEED 

SENSOR RH

VDC(diag)-41

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

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 connec-
tor.

Go to step 2.

2

CHECK HARNESS CONNECTOR BETWEEN 
VDCCM&H/U AND ABS WHEEL SPEED 
SENSOR.
1) Disconnect the connector (B310) from the 
VDCCM&H/U.
2) Disconnect the connector from the 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. 6 — (B6) No. 1:
(B310) No. 5 — (B6) No. 2:

DTC C0023

(B310) No. 1 — (B15) No. 1:
(B310) No. 26 — (B15) No. 2:

DTC C0025

(B310) No. 3 — (R72) No. 1:
(B310) No. 4 — (R72) No. 2:

DTC C0027

(B310) No. 2 — (R73) No. 1:
(B310) No. 27 — (R73) No. 2:

Is the resistance less than 0.5 

:? Go to step 3.

Repair the harness 
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. 6 — Chassis ground:

DTC C0023

(B310) No. 1 — Chassis ground:

DTC C0025

(B310) No. 4 — Chassis ground:

DTC C0027

(B310) No. 27 — Chassis ground:

Is the resistance 1 M

: or 

more?

Go to step 4.

Repair the harness 
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. 2 (+) — Chassis ground (–):

DTC C0023

(B15) No. 2 (+) — 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)-42

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)

E: DTC C0022 FRONT RIGHT ABS SENSOR SIGNAL

NOTE:
For the diagnostic procedure, refer to DTC C0028 “RL WHEEL SPEED SENSOR SIGNAL”. <Ref. to VDC(di-
ag)-43, DTC C0028 REAR LEFT ABS SENSOR SIGNAL, Diagnostic Procedure with Diagnostic Trouble
Code (DTC).>

F: DTC C0024 FRONT LEFT ABS SENSOR SIGNAL

NOTE:
For the diagnostic procedure, refer to DTC C0028 “RL WHEEL SPEED SENSOR SIGNAL”. <Ref. to VDC(di-
ag)-43, DTC C0028 REAR LEFT ABS SENSOR SIGNAL, Diagnostic Procedure with Diagnostic Trouble
Code (DTC).>

G: DTC C0026 REAR RIGHT ABS SENSOR SIGNAL

NOTE:
For the diagnostic procedure, refer to DTC C0028 “RL WHEEL SPEED SENSOR SIGNAL”. <Ref. to VDC(di-
ag)-43, DTC C0028 REAR LEFT ABS SENSOR SIGNAL, 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. 28 (+) — (B310) No. 25 (–):

Is the voltage 10 — 15 V?

Go to step 6.

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-14, ABS WHEEL SPEED SENSOR, 
INSPECTION, Front ABS Wheel Speed Sen-
sor.>

Is the pattern the same wave-
form as shown in the figure?

Go to step 7.

Replace the ABS 
wheel speed sen-
sor.

7

CHECK VDCCM&H/U.
1) Connect all connectors.
2) Clear the memory. <Ref. to VDC(diag)-23, 
Clear Memory Mode.>
3) Perform the Inspection Mode. <Ref. to 
VDC(diag)-22, PROCEDURE, Inspection 
Mode.>
4) Read the DTC. 

Is the same DTC displayed?

Replace the 
VDCCM only. 
<Ref. to VDC-10, 
REPLACEMENT, 
VDC Control Mod-
ule and Hydraulic 
Control Unit 
(VDCCM&H/U).>

Go to step 8.

8

CHECK OTHER DTC DETECTION.

Is any other DTC displayed?

Perform the diag-
nosis according to 
DTC. <Ref. to 
VDC(diag)-34, List 
of Diagnostic Trou-
ble Code (DTC).>

It results from a 
temporary noise 
interference.

Step

Check

Yes

No