Subaru Legacy III (2000-2003 year). Manual - part 129

EN(H4SO)-128

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

N: DTC P0121 — THROTTLE/PEDAL POSITION SENSOR/SWITCH “A” CIRCUIT 

RANGE/PERFORMANCE —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

• TROUBLE SYMPTOM:

• Erroneous idling
• Engine stalls.
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode<Ref. to EN(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-01126

19

13

3

9

11

12

2

3

4

E2

B21

E13

THROTTLE

POSITION

SENSOR

B21

1 2

3 4

5

6 7

8

9 10

11 12

13

14 15

16

17 18

19 20

B135 ECM

5 6 7

8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26

27 28

16 17 18 19

20 21

B135

B83

1 2 3 4 5 6

E13

1 2 3 4

B83

3

1

FG

2

4

EG

: FOR G.C.C COUNTRIES MODEL 

: EXCEPT FOR G.C.C COUNTRIES MODEL 

FG

EG

EN(H4SO)-129

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC displayed?

DTC indicated.

Inspect the rele-
vant DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H4SO)-83, List 
of Diagnostic 
Trouble Code 
(DTC).>

NOTE:
In this case, it is
not necessary to
inspect DTC
P0121.

Replace throttle 
position sensor.  
<Ref. to 
FU(H4SO)-30, 
Throttle Position 
Sensor.>

EN(H4SO)-130

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

O:  DTC P0122 — THROTTLE/PEDAL POSITION SENSOR/SWITCH “A” CIR-

CUIT LOW INPUT —

• DTC DETECTING CONDITION:

• Immediately at fault recognition

• TROUBLE SYMPTOM:

• Erroneous idling
• Engine stalls.
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode<Ref. to EN(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-01126

19

13

3

9

11

12

2

3

4

E2

B21

E13

THROTTLE

POSITION

SENSOR

B21

1 2

3 4

5

6 7

8

9 10

11 12

13

14 15

16

17 18

19 20

B135 ECM

5 6 7

8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26

27 28

16 17 18 19

20 21

B135

B83

1 2 3 4 5 6

E13

1 2 3 4

B83

3

1

FG

2

4

EG

: FOR G.C.C COUNTRIES MODEL 

: EXCEPT FOR G.C.C COUNTRIES MODEL 

FG

EG

EN(H4SO)-131

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK CURRENT DATA.
1) Start engine.
2) Read data of throttle position sensor signal 

using Subaru Select Monitor or OBD-II gen-
eral scan tool.
Is the measured value less than the speci-
fied value?

NOTE:

•Subaru Select Monitor
For detailed operation procedure, refer to the 
“READ CURRENT DATA FOR ENGINE”. 
<Ref. to EN(H4SO)-32, Subaru Select Moni-
tor.>  
•OBD-II general scan tool
For detailed operation procedures, refer to the 
OBD-II General Scan Tool Instruction Manual.

0.1 V

Go to step 2.

Even if MI lights 
up, the circuit has 
returned to a nor-
mal condition at 
this time. A tempo-
rary poor contact 
of the connector 
may be the cause.

NOTE:
In this case, repair
the following:
• Poor contact in 
throttle position 
sensor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector

2

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM connector and 
chassis ground while throttle valve is fully 
closed.

Connector & terminal

(B135) No. 3 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

4.5 V

Go to step 4.

Go to step 3.

3

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B135) No. 3 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value by shaking harness and connector of 
ECM while monitoring the value with voltage 
meter?

4.5 V

Repair poor con-
tact in ECM con-
nector.

Contact SUBARU 
distributor service.

NOTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.

4

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B135) No. 13 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified 
value?

0.1 V

Go to step 6.

Go to step 5.

5

CHECK INPUT SIGNAL FOR ECM. (USING 
SUBARU SELECT MONITOR.)
Measure voltage between ECM connector and 
chassis ground.
Does the measured value exceed the specified 
value by shaking harness and connector of 
ECM while monitoring the value with Subaru 
Select Monitor?

0.1 V

Repair poor con-
tact in ECM con-
nector.

Go to step 6.