Subaru Legacy III (2000-2003 year). Manual - part 164

EN(H4SO)-268

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

BQ:DTC P0865 — TCM COMMUNICATION CIRCUIT LOW —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

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-01138

19

21

B137 ECM

TCM

B56

B137

4

1
5

3

2
6

18

15

16

7 8 9 10 11

17

19 20

12 13

14

B56

1 2

7

8

9

5 6

3 4

10 11 12
19 20 21

13

14 15

16

17

18

22

23

24

EN(H4SO)-269

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
1) Turn ignition switch to ON.
2) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

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

1 V

Go to step 2.

Even if MI lights 
up, the circuit has 
returned to a nor-
mal condition at 
this time.

NOTE:
In this case, repair
the following:
• Poor contact in 
ECM connector
• Poor contact in 
TCM connector

2

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM and TCM.
3) Measure resistance of harness between 

ECM and chassis ground.

Connector & terminal

(B137) No. 19 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 3.

Repair ground 
short circuit in har-
ness between 
ECM and TCM 
connector.

3

CHECK OUTPUT SIGNAL FOR ECM.
1) Connect connector to ECM.
2) Turn ignition switch to ON.
3) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

5 V

Go to step 4.

Repair poor con-
tact in ECM con-
nector.

4

CHECK TROUBLE CODE FOR AUTOMATIC 
TRANSMISSION.
Read trouble code for automatic transmission. 
<Ref. to AT-24, Read Diagnostic Trouble Code 
(DTC).>
Does trouble code appear for automatic trans-
mission?

Trouble code indicated.

Inspect trouble 
code for auto-
matic transmis-
sion. <Ref. to AT-
42, Diagnostic 
Procedure with 
Diagnostic Trou-
ble Code (DTC).>

Replace TCM. 
<Ref. to AT-76, 
Transmission Con-
trol Module 
(TCM).>

EN(H4SO)-270

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

BR:DTC P0866 — TCM COMMUNICATION CIRCUIT HIGH —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

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-01138

19

21

B137 ECM

TCM

B56

B137

4

1
5

3

2
6

18

15

16

7 8 9 10 11

17

19 20

12 13

14

B56

1 2

7

8

9

5 6

3 4

10 11 12
19 20 21

13

14 15

16

17

18

22

23

24

EN(H4SO)-271

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
1) Turn ignition switch to ON.
2) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Repair battery 
short circuit in har-
ness between 
ECM and TCM 
connector. After 
repair, replace 
ECM. <Ref. to 
FU(H4SO)-45, 
Engine Control 
Module.>

Go to step 2.

2

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

4 V

Go to step 5.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified 
value?

1 V

Repair poor con-
tact in ECM con-
nector.

Go to step 4.

4

CHECK OUTPUT SIGNAL FROM ECM.
Measure voltage between ECM and chassis 
ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value change within the 
specified range?

1 V - 4 V

Even if MI lights 
up, the circuit has 
returned to a nor-
mal condition at 
this time.

NOTE:
In this case, repair
the following:
• Poor contact in 
ECM connector
• Poor contact in 
TCM connector

Contact SUBARU 
distributor service.

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

5

CHECK HARNESS BETWEEN ECM AND 
TCM CONNECTOR.
Measure voltage between TCM and chassis 
ground.

Connector & terminal

(B56) No. 21 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

4 V

Go to step 6.

Repair open circuit 
in harness 
between ECM and 
TCM connector.

6

CHECK POOR CONTACT.
Check poor contact in TCM connector.
Is there poor contact in TCM connector?

There is poor contact.

Repair poor con-
tact in TCM con-
nector.

Check TCM power 
supply line and 
grounding line.