Subaru Legacy III (2000-2003 year). Manual - part 483

EN(H4DOSTC)-102

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

4

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
Measure the voltage between engine coolant 
temperature sensor connector and engine 
ground.

Connector & terminal

(E8) No. 2 (+) — Engine ground (

−−−−

):

Does the measured value exceed the specified 
value?

4 V

Go to step 5.

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector
• Poor contact in 
engine coolant 
temperature sen-
sor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

5

CHECK HARNESS BETWEEN ENGINE 
COOLANT TEMPERATURE SENSOR AND 
ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness 

between engine coolant temperature sen-
sor connector and engine ground.

Connector & terminal

(E8) No. 1 — Engine ground:

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

5 

Ω

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H4DOSTC)-
28, Engine Cool-
ant Temperature 
Sensor.>

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:

• Open circuit in 
harness between 
ECM and engine 
coolant tempera-
ture sensor con-
nector
• Poor contact in 
engine coolant 
temperature sen-
sor connector
• Poor contact in 
ECM connector
• Poor contact in 
coupling connector
• Poor contact in 
joint connector

Step

Value

Yes

No

EN(H4DOSTC)-103

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO:

EN(H4DOSTC)-104

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

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

CUIT LOW INPUT —

• TROUBLE SYMPTOM:

• Erroneous idling
• Engine stalls.
• Poor driving performance

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-00937

E2

E13

B21

B122

THROTTLE
 POSITION
  SENSOR

1

3

2

20

19

18

6

1

B135 ECM

9

19

7

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

E13

1 2 3

B21

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

B122

1 2 3 4 5 6

EN(H4DOSTC)-105

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

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

signal using Subaru Select Monitor.
Is the measured value less than the speci-
fied value?

NOTE:

For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOSTC)-26, Subaru Select Monitor.>  

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 the voltage between ECM connector 
and chassis ground while throttle valve is fully 
closed.

Connector & terminal

(B135) No. 9 (+) — 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 the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B135) No. 9 (+) — Chassis ground (

−−−−

):

Does the measured value change by shaking 
harness and connector of ECM while monitor-
ing the value with voltage meter?

The voltage changes.

Repair the poor 
contact in ECM 
connector.

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 the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B135) No. 7 (+) — 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 the voltage between ECM connector 
and chassis ground.
Does the measured value change by shaking 
harness and connector of ECM while monitor-
ing the value with Subaru Select Monitor?

The value changes.

Repair the poor 
contact in ECM 
connector.

Go to step 6.