Subaru Legacy III (2000-2003 year). Service manual — part 497

EN(H4DOSTC)-158

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AH:DTC P0508 — IDLE CONTROL SYSTEM CIRCUIT LOW —

• TROUBLE SYMPTOM:

• Erroneous idling
• Engine stalls.
• Engine breathing

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H4DOSTC)-35,
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOSTC)-33, Inspection
Mode.> .
• WIRING DIAGRAM:

EN-00947

BATTERY

MAIN RELAY

E

E

6
4

5
3

2
1

10

IDLE
AIR CONTROL
SOLENOID
VALVE

1

3

E7

B47

B47

3

4

1

2

5

6

1 2

7

8 9

5

6

3

4

10 11 12
19 20 21

13 14 15 16

17 18

22 23 24

B136

B136 ECM

2

1

B22

E3

SBF-5

B22

E7

1 2 3

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B21

E2

B21

12

EN(H4DOSTC)-159

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK OUTPUT SIGNAL FROM ECM.
1) Turn the ignition switch to ON.
2) Measure the voltage between ECM and

chassis ground.

Connector & terminal

(B136) No. 10 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

3 V

Repair the poor
contact in ECM
connector.

Go to step 2.

2

CHECK POWER SUPPLY TO IDLE AIR CON-
TROL SOLENOID VALVE.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from idle air con-

trol solenoid valve.

3) Turn the ignition switch to ON.
4) Measure the voltage between idle air con-

trol solenoid valve and engine ground.

Connector & terminal

(E7) No. 2 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Go to step 3.

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit in
harness between
idle air control
solenoid valve and
main relay con-
nector
• Poor contact in
coupling connector

3

CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness

between ECM and idle air control solenoid
valve connector.

Connector & terminal

(B136) No. 10 — (E7) No. 1:

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

1

Ω

Go to step 4.

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and idle air
control solenoid
valve connector
• Poor contact in
coupling connector

4

CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
Measure the resistance of harness between
ECM and chassis ground.

Connector & terminal

(B136) No. 10 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 5.

Repair the ground
short circuit in har-
ness between
ECM and idle air
control solenoid
valve connector.

5

CHECK GROUND CIRCUIT OF IDLE AIR
CONTROL SOLENOID VALVE.
Measure the resistance of harness between
idle air control solenoid valve connector and
engine ground.

Connector & terminal

(E7) No. 3 — Engine ground:

Is the measured value less than the specified
value?

5

Ω

Go to step 6.

Repair the open
circuit in harness
between idle air
control solenoid
valve connector
and engine ground
cable.

EN(H4DOSTC)-160

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

CHECK POOR CONTACT.
Check poor contact in ECM and idle air control
solenoid valve connectors.
Is there poor contact in ECM and idle air con-
trol solenoid valve connectors?

There is poor contact.

Repair the poor
contact in ECM
and idle air control
solenoid valve
connectors.

Replace the idle
air control solenoid
valve. <Ref. to
FU(H4DOSTC)-
35, Idle Air Con-
trol Solenoid
Valve.>

Step

Value

Yes

No

EN(H4DOSTC)-161

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO: