Subaru Legacy (2005 year). Service manual - part 347

EN(H4DOTC)(diag)-157

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AX:DTC P0638 THROTTLE ACTUATOR CONTROL RANGE/PERFORMANCE 

(BANK 1)

NOTE:
For the diagnostic procedure, refer to DTC P2101. <Ref. to EN(H4DOTC)(diag)-183, DTC P2101 THROT-
TLE ACTUATOR CONTROL MOTOR CIRCUIT RANGE/PERFORMANCE, Diagnostic Procedure with Di-
agnostic Trouble Code (DTC).>

AY:DTC P0700 TRANSMISSION CONTROL SYSTEM (MIL REQUEST)

NOTE:
For the diagnostic procedure, refer to AT section. <Ref. to 5AT(diag)-2, Basic Diagnostic Procedure.>

2

CHECK INPUT VOLTAGE OF ECM.
1) Start the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.

Connector & terminal

(B135) No. 5 (+) — Chassis ground (

−

):

(B135) No. 6 (+) — Chassis ground (

−

):

Is the voltage 13 — 15 V?

Go to step 3.

Repair the open or 
ground short cir-
cuit of power sup-
ply circuit.

3

CHECK ECM GROUND HARNESS.
Measure the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B137) No. 1 (+) — Chassis ground (

−

):

(B137) No. 2 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Repair the poor 
contact in ECM 
connector. 
Replace the ECM 
if defective. <Ref. 
to FU(H4DOTC)-
34, Engine Con-
trol Module 
(ECM).>

Further tighten the 
engine ground ter-
minal.

Step

Check

Yes

No

EN(H4DOTC)(diag)-158

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AZ:DTC P0851 PARK/NEUTRAL SWITCH INPUT CIRCUIT LOW

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
TROUBLE SYMPTOM:
Erroneous idling

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-
37, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOTC)(diag)-30, PROCE-
DURE, Inspection Mode.>.
WIRING DIAGRAM:

ECM

9

2

B25

T2

T2

B25

1

EN-03558

B55

NEUTRAL
POSITION
SWITCH

B137

19

TCM

B55

B137

5

6

7

8

2

1

9

4

3

10

22 23

11 12 13 14 15

24 25

26

16 17

18 19 20 21

27

28 29

30 31

AT

MT

1 2 3 4

10 11 12
19 20 21

13

5 6

14 15

7

8

9

16

17

18

22

23

24

E

B25

1 2

EN(H4DOTC)(diag)-159

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK TRANSMISSION TYPE.

Is the transmission type AT?

Go to step 2.

Go to step 5.

2

CHECK DTC.
Check the DTC of AT.

Is DTC of AT displayed?

Perform the diag-
nosis for AT. <Ref. 
to 5AT(diag)-35, 
Diagnostic Proce-
dure with Diagnos-
tic Trouble Code 
(DTC).>

Go to step 3.

3

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

Connector & terminal

(B137) No. 9 — (B55) No. 19:

Is the resistance less than 1 
Ω?

Go to step 4.

Repair the open 
circuit of harness 
between ECM and 
TCM.

4

CHECK HARNESS BETWEEN ECM AND 
TCM.
Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B137) No. 9 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Repair the poor 
contact in ECM 
and TCM connec-
tor.

Repair the ground 
short circuit of har-
ness between 
ECM and TCM.

5

CHECK INPUT SIGNAL OF ECM.
1) Turn the ignition switch to ON.
2) Place the shift lever in neutral.
3) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B137) No. 9 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 6.

Go to step 7.

6

CHECK INPUT SIGNAL OF ECM.
1) Place the shift lever except in neutral.
2) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B137) No. 9 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Repair the poor 
contact in ECM 
connector.

Go to step 7.

7

CHECK NEUTRAL POSITION SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from transmis-
sion harness.
3) Place the shift lever in neutral.
4) Measure the resistance between transmis-
sion harness and connector terminals.

Connector & terminal

(T2) No. 1 — No. 3:

Is the resistance more than 1 
M

Ω?

Go to step 8.

Repair the short 
circuit in transmis-
sion harness, or 
replace the neu-
tral position switch.

8

CHECK NEUTRAL POSITION SWITCH.
1) Place the shift lever except in neutral.
2) Measure the resistance between transmis-
sion harness connector terminals.

Is the resistance less than 1 
Ω?

Go to step 9.

Repair the short 
circuit in transmis-
sion harness, or 
replace the neu-
tral position switch.

9

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B137) No. 9 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 10.

Repair the ground 
short circuit of har-
ness between 
ECM and trans-
mission harness 
connector.

EN(H4DOTC)(diag)-160

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

10

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
1) Disconnect the connector from ECM.
2) Measure the resistance of harness 
between ECM and transmission harness con-
nector.

Connector & terminal

(B137) No. 9 — (B25) No. 1:

Is the resistance less than 1 
Ω?

Go to step 11.

Repair the open 
circuit of harness 
between ECM and 
transmission har-
ness connector.

11

CHECK HARNESS BETWEEN NEUTRAL 
POSITION SWITCH CONNECTOR AND EN-
GINE GROUND.
Measure the resistance of harness between 
transmission harness connector and engine 
ground.

Connector & terminal

(B25) No. 2 — Engine ground:

Is the resistance less than 1 
Ω?

Go to step 12.

Repair the open 
circuit between 
transmission har-
ness connector 
and engine ground 
terminal.

12

CHECK POOR CONTACT.
Check poor contact in transmission harness 
connector.

Is there poor contact in trans-
mission harness connector?

Repair the poor 
contact in trans-
mission harness 
connector.

Replace the ECM. 
<Ref. to 
FU(H4DOTC)-34, 
Engine Control 
Module (ECM).>

Step

Check

Yes

No