Subaru Legacy IV (2008 year). Service manual — part 136
EN(H4SO)(diag)-147
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
AF:DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 2)
DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-55, DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE
(BANK 1 SENSOR 2), Diagnostic Trouble Code (DTC) Detecting Criteria.>
CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:
EN-06836
A5
D1
D2
D3
D7
36
34
35
37
52
ECM
B21
B138
E2
B135
B:
D: B137
C: B136
E
E
A: B134
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
B134
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
33 34
29
32
30 31
B136
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
33 34
29
32
30
31
35
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
29 30 31
32 33
34 35
A:
B:
C:
D:
*
*
3
4
1
2
5
6
B327
SBF-5
E
B327
E23
6
4
5
3
2
1
1
B21
E2
50
53
1
19
E2
B21
E
E23
BATTERY
REAR OXYGEN
SENSOR
A/F, OXYGEN
SENSOR RELAY
1
3 4
2
2
3
4
B1
B4
A29
C4
B138
3 4
5 6
1 2
7 8
B21
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31 32 33
34
35
42
43
36
37
38
39
48
49
50
51
52
53
54
40
41
44
45
46
47
: TERMINAL No. OPTIONAL
ARRANGEMENT
*
EN(H4SO)(diag)-148
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
Check
Yes
No
1
CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is above 75°C (167°F), and keep
the engine speed at 3,000 rpm. (for up to 2 min-
utes)
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or general scan
tool.
NOTE:
• SUBARU SELECT MONITOR
For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4SO)(diag)-33, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.
Is the voltage 490 mV or more? Go to step 5.
Go to step 2.
2
CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.
Has water entered the connec-
tor?
Completely
remove any water
inside.
Go to step 3.
3
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and
rear oxygen sensor.
3) Measure the resistance of harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 4 — (E23) No. 3:
(B134) No. 29 — (E23) No. 4:
Is the resistance less than 1
:? Go to step 4.
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector
4
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor connector and chassis ground.
Connector & terminal
(E23) No. 3 (+) — Chassis ground (–):
Is the voltage 0.2 — 0.5 V?
Replace the rear
oxygen sensor.
<Ref. to
FU(H4SO)-37,
Rear Oxygen Sen-
sor.>
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
the ECM and rear
oxygen sensor
• Poor contact of
the rear oxygen
sensor connector
• Poor contact in
ECM connector
5
CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Looseness and improper attachment of ex-
haust system parts
• Damage (crack, hole etc.) of parts
• Looseness and improper attachment of parts
between front oxygen (A/F) sensor and rear ox-
ygen sensor
Is there any fault in exhaust
system?
Repair or replace
faulty parts.
Replace the rear
oxygen sensor.
<Ref. to
FU(H4SO)-37,
Rear Oxygen Sen-
sor.>
EN(H4SO)(diag)-149
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
AG:DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)
DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-57, DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE
(BANK 1 SENSOR 2), Diagnostic Trouble Code (DTC) Detecting Criteria.>
CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:
EN-06836
A5
D1
D2
D3
D7
36
34
35
37
52
ECM
B21
B138
E2
B135
B:
D: B137
C: B136
E
E
A: B134
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
B134
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
33 34
29
32
30 31
B136
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
33 34
29
32
30
31
35
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
29 30 31
32 33
34 35
A:
B:
C:
D:
*
*
3
4
1
2
5
6
B327
SBF-5
E
B327
E23
6
4
5
3
2
1
1
B21
E2
50
53
1
19
E2
B21
E
E23
BATTERY
REAR OXYGEN
SENSOR
A/F, OXYGEN
SENSOR RELAY
1
3 4
2
2
3
4
B1
B4
A29
C4
B138
3 4
5 6
1 2
7 8
B21
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31 32 33
34
35
42
43
36
37
38
39
48
49
50
51
52
53
54
40
41
44
45
46
47
: TERMINAL No. OPTIONAL
ARRANGEMENT
*
EN(H4SO)(diag)-150
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
Check
Yes
No
1
CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is above 75°C (167°F), and rapidly
reduce the engine speed from 3,000 rpm.
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or general scan
tool.
NOTE:
• SUBARU SELECT MONITOR
For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4SO)(diag)-33, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.
Is the voltage 250 mV or less?
Go to step 5.
Go to step 2.
2
CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.
Has water entered the connec-
tor?
Completely
remove any water
inside.
Go to step 3.
3
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and
rear oxygen sensor.
3) Measure the resistance of harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 4 — (E23) No. 3:
(B134) No. 29 — (E23) No. 4:
Is the resistance less than 1
:? Go to step 4.
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector
4
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor connector and chassis ground.
Connector & terminal
(E23) No. 3 (+) — Chassis ground (–):
Is the voltage 0.2 — 0.5 V?
Replace the rear
oxygen sensor.
<Ref. to
FU(H4SO)-37,
Rear Oxygen Sen-
sor.>
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
the ECM and rear
oxygen sensor
• Poor contact of
the rear oxygen
sensor connector
• Poor contact in
ECM connector
5
CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Looseness and improper attachment of ex-
haust system parts
• Damage (crack, hole etc.) of parts
• Looseness and improper attachment of parts
between front oxygen (A/F) sensor and rear ox-
ygen sensor
Is there any fault in exhaust
system?
Repair or replace
faulty parts.
Replace the rear
oxygen sensor.
<Ref. to
FU(H4SO)-37,
Rear Oxygen Sen-
sor.>
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