Subaru Legacy III (2000-2003 year). Manual — part 221

EN(H4SOw/oOBD)-74

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

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

solenoid valve.

3) Turn ignition switch to ON.
4) Measure voltage between idle air control

solenoid valve connector and engine
ground.

Connector & terminal

(E7) No. 2 (+) — Engine ground (

−−−−

):

(E7) No. 5 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Go to step 2.

Repair harness
and connector.

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
(B22)

2

CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
1) Turn ignition switch to OFF.
2) Measure resistance between ECM and idle

air control solenoid valve connector.

Connector & terminal

#1; (B134) No. 20 — (E7) No. 3:
#2; (B134) No. 6 — (E7) No. 1:
#3; (B134) No. 19 — (E7) No. 6:
#4; (B134) No. 5 — (E7) No. 4:

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

1

Ω

Go to step 3.

Repair harness
and connector.

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
(B21)

3

CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
1) Disconnect connector from ECM.
2) Measure resistance between ECM connec-

tor and chassis ground.

Connector & terminal

#1; (B134) No. 20 — Chassis ground:
#2; (B134) No. 6 — Chassis ground:
#3; (B134) No. 19 — Chassis ground:
#4; (B134) No. 5 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 4.

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

4

CHECK POOR CONTACT.
Check poor contact in ECM connector and idle
air control solenoid valve connector.
Is there poor contact in ECM connector or idle
air control solenoid valve connector?

There is poor contact.

Repair poor con-
tact in ECM con-
nector or idle air
control solenoid
valve connector.

Go to step 5.

5

CHECK SPECIFICATIONS.
Is the vehicle equipped with rear catalytic con-
verter?

Equipped with rear catalytic
converter.

Go to step 7.

Go to step 6.

6

CHECK IDLE SPEED.
Is idling speed within the specified value?

550 — 750 rpm

Go to step 8.

Go to step 10.

7

CHECK IDLE SPEED.
Is idling speed within the specified value?

600 — 800 rpm

Go to step 8.

Go to step 10.

EN(H4SOw/oOBD)-75

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

8

CHECK AIR INTAKE SYSTEM.
1) Turn ignition switch to ON.
2) Start engine, and idle it.
3) Check the following items.
• Loose installation of intake manifold, idle air
control solenoid valve and throttle body
• Cracks of intake manifold gasket, idle air con-
trol solenoid valve gasket and throttle body
gasket
• Disconnections of vacuum hoses

Is there a fault in air intake system?

The system is faulty.

Repair air suction
and leaks.

Go to step 9.

9

CHECK AIR BY-PASS LINE.
1) Turn ignition switch to OFF.
2) Remove idle air control solenoid valve from

throttle body. <Ref. to FU(H4SOw/oOBD)-
33, Idle Air Control Solenoid Valve.>

3) Confirm that there are no foreign particles

in by-pass air line.
Are foreign particles in by-pass air line?

Foreign particles in by-pass air
line.

Remove foreign
particles from by-
pass air line.

Replace idle air
control solenoid
valve. <Ref. to
FU(H4SOw/
oOBD)-33, Idle Air
Control Solenoid
Valve.>

10

CHECK AIR BY-PASS LINE.
1) Turn ignition switch to OFF.
2) Remove idle air control solenoid valve from

throttle body. <Ref. to FU(H4SOw/oOBD)-
33, Idle Air Control Solenoid Valve.>

3) Remove throttle body from intake mani-

fold. <Ref. to FU(H4SOw/oOBD)-13,
Throttle Body.>

4) Confirm that there are no foreign particles

in the throttle body.

5) Using an air gun, force air into idle air con-

trol solenoid valve installation area. Confirm
that forced air subsequently escapes from
throttle body interior.
Does air flow out?

Air flows out.

Replace idle air
control solenoid
valve. <Ref. to
FU(H4SOw/
oOBD)-33, Idle Air
Control Solenoid
Valve.>

Replace throttle
body. <Ref. to
FU(H4SOw/
oOBD)-13, Throt-
tle Body.>

Step

Value

Yes

No

EN(H4SOw/oOBD)-76

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

G: DTC 26 INTAKE AIR TEMPERATURE SENSOR

• DIAGNOSIS:

• The intake air temperature sensor signal is abnormal.
• The harness connector between ECM and intake air temperature sensor is in short or open.

• TROUBLE SYMPTOM:

• Hard to start
• Erroneous idling
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, conduct CLEAR MEMORY and INSPECTION MODES. <Ref.
to EN(H4SOw/oOBD)-28, OPERATION, Clear Memory Mode.> and <Ref. to EN(H4SOw/oOBD)-26, OP-
ERATION, Inspection Mode.>
• WIRING DIAGRAM:

EN-01055

16

15

13

5

INTAKE AIR

TEMPERATURE

AND

PRESSURE

SENSOR

4
6

5

4

6 7

8

2

1

9

3

10

22

23

11 12 13 14 15

24 25

26 27

16 17 18

28 29

19 20

21

30

B136

B83

9

15

14

12

B21

E2

1

4

2

3

E21

B83

E20

1 2 3 4

ECM

B21

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

B136

EN(H4SOw/oOBD)-77

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK INTAKE AIR TEMPERATURE SEN-
SOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from intake air tem-

perature sensor.

3) Measure resistance between intake air

temperature sensor terminals.

Terminals

No. 2 — No. 3:

Is resistance within the specified value at
20

°

C (68

°

F)?

2 — 3 k

Ω

Go to step 2.

Replace intake air
temperature sen-
sor. <Ref. to
FU(H4SOw/
oOBD)-32, Intake
Air Temperature
and Pressure Sen-
sor.>

2

CHECK INTAKE AIR TEMPERATURE SEN-
SOR.
Measure resistance between intake air tem-
perature sensor terminals.

Terminals

No. 2 — No. 3:

Is resistance within the specified value at 50

°

C

(122

°

F)?

0.66 — 1 k

Ω

Go to step 3.

Replace intake air
temperature sen-
sor. <Ref. to
FU(H4SOw/
oOBD)-32, Intake
Air Temperature
and Pressure Sen-
sor.>

3

CHECK HARNESS BETWEEN ECM AND IN-
TAKE AIR TEMPERATURE SENSOR CON-
NECTOR.
1) Disconnect connector from ECM.
2) Measure resistance of harness connector

between ECM and intake air temperature
sensor connector.

Connector & terminal

(B136) No. 15 — (E20) No. 3:

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

1

Ω

Go to step 4.

Repair harness
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and intake
air temperature
and pressure sen-
sor connector
• Poor contact in
coupling connector
(B21)

4

CHECK HARNESS BETWEEN ECM AND IN-
TAKE AIR TEMPERATURE SENSOR CON-
NECTOR.
Measure resistance of harness connector
between ECM and intake air temperature sen-
sor connector.

Connector & terminal

(B136) No. 13 — (E21) No. 2:

Is the measured value less than the specified
value?

1

Ω

Go to step 5.

Repair harness
and connector.

5

CHECK HARNESS BETWEEN ECM AND IN-
TAKE AIR TEMPERATURE SENSOR CON-
NECTOR.
Measure resistance of harness between ECM
connector and chassis ground.

Connector & terminal

(B136) No. 15 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 6.

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