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.