Subaru Legacy III (2000-2003 year). Manual - part 337

EN(H6DO)-150

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

R:  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(H6DO)-54, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)-47, OPERATION, Inspec-
tion Mode.>.

• WIRING DIAGRAM:

EN-00814

19

7

9

13

15

16

1

2

3

E1

B20

E13

THROTTLE

POSITION

SENSOR

E13

1 2 3

5

8

B83

B20

B135

ECM

B83

B135

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

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

1 2 3 4

5 6 7 8 9 10

11 12

19 20

13 14 15 16 17 18

EN(H6DO)-151

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(H6DO)-34, 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. 7 (+) — 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. 7 (+) — Chassis ground (

−−−−

):

Does the voltage change more than the speci-
fied 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. 9 (+) — 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 voltage change more than the speci-
fied 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.

EN(H6DO)-152

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

CHECK HARNESS BETWEEN ECM AND 
THROTTLE POSITION SENSOR CONNEC-
TOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from throttle posi-

tion sensor.

3) Turn ignition switch to ON.
4) Measure voltage between throttle position 

sensor connector and engine ground.

Connector & terminal

(E13) No. 1 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

4.5 V

Go to step 7.

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
throttle position 
sensor and ECM 
connector
• Poor contact in 
throttle position 
sensor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

7

CHECK HARNESS BETWEEN ECM AND 
THROTTLE POSITION SENSOR CONNEC-
TOR.
1) Turn ignition switch to OFF.
2) Measure resistance of harness between 

ECM connector and throttle position sensor 
connector.

Connector & terminal

(B135) No. 9 — (E13) No. 3:

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

1 

Ω

Go to step 8.

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
throttle position 
sensor and ECM 
connector
• Poor contact in 
ECM connector
• Poor contact in 
throttle position 
sensor connector
• Poor contact in 
coupling connector

8

CHECK HARNESS BETWEEN ECM AND 
THROTTLE POSITION SENSOR CONNEC-
TOR.
Measure resistance of harness between throt-
tle position sensor connector and engine 
ground.

Connector & terminal

(E13) No. 3 — Engine ground:

Is the measured value less than the specified 
value?

10 

Ω

Repair ground 
short circuit in har-
ness between 
throttle position 
sensor and ECM 
connector.

Go to step 9.

9

CHECK POOR CONTACT.
Check poor contact in throttle position sensor 
connector. 
Is there poor contact in throttle position sensor 
connector?

There is poor contact.

Repair poor con-
tact in throttle posi-
tion sensor 
connector.

Replace throttle 
position sensor. 
<Ref. to 
FU(H6DO)-33, 
Throttle Position 
Sensor.>

Step

Value

Yes

No

EN(H6DO)-153

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO: