Subaru Legacy (2005 year). Service manual — part 334
EN(H4DOTC)(diag)-105
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
R: DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 2)
DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
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:
EN-03555
1 2 3 4
5 6 7 8
B83
BATTERY
MAIN RELAY
B47
1
2
4
6
3
5
E
E
B21
E2
35
*
*
B83
3
4
1
2
5
6
B135
B47
B19
B136
1
4
2
3
T6
REAR
OXYGEN SENSOR
B4
B1
B2
D25
D31
C35
ECM
B136
B137
C:
B135
B:
D:
1
2
3
4
B:
C:
B137
D:
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
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
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
B19
T5
2
T5
B19
3
1
4
B21
1 2 3 4
12 13 14 15
5 6 7 8
16 17 18 19
9 10 11
20 21 22
23 24 25 26 27 28 29 30 31 32 33
35
34
37
36
39
38
41
40
43
42
44
45
47
46
49
48
51
50
53
52
54
T6
2 1
4 3
*
: TERMINAL No. RANDOM ARRANGEMENT
EN(H4DOTC)(diag)-106
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
Check
Yes
No
1
CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC displayed?
Check DTC using
“List of Diagnostic
Trouble Code
(DTC)”. <Ref. to
EN(H4DOTC)(diag
)-62, List of Diag-
nostic Trouble
Code (DTC).>
2
CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant
temperature is above 70
°C (158°F), and keep
the engine speed at 2,000 to 3,000 rpm for two
minutes.
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(H4DOTC)(diag)-24, Subaru Select Mon-
itor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual.
Does the value fluctuate?
3
CHECK REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen sensor signal
using Subaru Select Monitor.
Is the voltage 0.2 — 0.4 V?
Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOTC)-33,
Rear Oxygen Sen-
sor.>
4
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
rear oxygen sensor.
3) Measure the resistance of harness
between ECM and rear oxygen sensor con-
nector.
Connector & terminal
(B137) No. 25 — (T6) No. 4:
Is the resistance more than 3
Ω?
Repair the open
circuit of harness
between ECM and
rear oxygen sen-
sor connector.
5
CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
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 harness connector and chassis ground.
Connector & terminal
(T6) No. 4 (+) — Chassis ground (
−
):
Is the voltage more than 0.2 V? Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOTC)-33,
Rear Oxygen Sen-
sor.>
Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit of
harness between
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
ECM connector
EN(H4DOTC)(diag)-107
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
6
CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Loose part and incomplete installation of
exhaust system
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between
front oxygen (A/F) sensor and rear oxygen
sensor
Is there any fault in exhaust
system?
Repair or replace
faulty parts.
Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOTC)-33,
Rear Oxygen Sen-
sor.>
Step
Check
Yes
No
EN(H4DOTC)(diag)-108
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
S: DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)
DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
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:
EN-03555
1 2 3 4
5 6 7 8
B83
BATTERY
MAIN RELAY
B47
1
2
4
6
3
5
E
E
B21
E2
35
*
*
B83
3
4
1
2
5
6
B135
B47
B19
B136
1
4
2
3
T6
REAR
OXYGEN SENSOR
B4
B1
B2
D25
D31
C35
ECM
B136
B137
C:
B135
B:
D:
1
2
3
4
B:
C:
B137
D:
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
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
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
B19
T5
2
T5
B19
3
1
4
B21
1 2 3 4
12 13 14 15
5 6 7 8
16 17 18 19
9 10 11
20 21 22
23 24 25 26 27 28 29 30 31 32 33
35
34
37
36
39
38
41
40
43
42
44
45
47
46
49
48
51
50
53
52
54
T6
2 1
4 3
*
: TERMINAL No. RANDOM ARRANGEMENT
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