Subaru Legacy (2005 year). Service manual — part 120
EN(H4SO 2.0)(diag)-69
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
18.Diagnostic Procedure with Diagnostic Trouble Code (DTC)
A: DTC P0030 HO2S HEATER CONTROL CIRCUIT (BANK 1 SENSOR 1)
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(H4SO 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:
EN-03475
3
4
1
2
5
6
B47
SBF-5
E
B47
E24
5
3
4
6
2
1
C34
C35
C33
B3
B2
B1
B135
E
B5
B6
52
B21
E2
B21
E2
50
51
3
4
E2
B21
E
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
E24
ECM
BATTERY
FRONT OXYGEN
(A/F) SENSOR
MAIN RELAY
B136
B:
C:
1
2
3
4
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
B:
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
C:
E24
3
2
*
1
*
*
3
LHD : 4
RHD : 1
*
1
*
*
2
3
3
1
6 5 4
2
: RHD
: LHD
LHD : 1
RHD : 4
LHD : 2
RHD : 6
EN(H4SO 2.0)(diag)-70
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
Check
Yes
No
1
CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Start and warm-up the engine.
2) Turn the ignition switch to OFF.
3) Disconnect the connectors from ECM and
front oxygen (A/F) sensor.
4) Measure the resistance of harness
between ECM and front oxygen (A/F) sensor
connector.
Connector & terminal
(B135) No. 2 — (E24) No. 3:
(B135) No. 3 — (E24) No. 3:
Is the resistance less than 1
Ω?
Repair the open
circuit of harness
between ECM and
front oxygen (A/F)
sensor connector.
2
CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance of harness between
ECM and front oxygen (A/F) sensor connector.
Connector & terminal
LHD model
(B136) No. 33 — (E24) No. 1:
(B136) No. 35 — (E24) No. 2:
RHD model
(B136) No. 33 — (E24) No. 4:
(B136) No. 35 — (E24) No. 6:
Is the resistance less than 1
Ω?
Repair the open
circuit of harness
between ECM and
front oxygen (A/F)
sensor connector.
3
CHECK HARNESS BETWEEN MAIN RELAY
AND FRONT OXYGEN (A/F) SENSOR CON-
NECTOR.
Measure the resistance of harness between
main relay and front oxygen (A/F) sensor con-
nector.
Connector & terminal
LHD model
(B47) No. 3 — (E24) No. 4:
RHD model
(B47) No. 3 — (E24) No. 1:
Is the resistance less than 1
Ω?
Repair the open
circuit of harness
between ECM and
front oxygen (A/F)
sensor connector.
4
CHECK FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between front oxygen
(A/F) sensor connector terminals.
Terminals
LHD model
No. 3 — No. 4:
RHD model
No. 1 — No. 3:
Is the resistance less than 5
Ω?
Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4SO 2.0)-32,
Front Oxygen (A/
F) Sensor.>
5
CHECK POOR CONTACT.
Check poor contact in ECM and front oxygen
(A/F) sensor connector.
Is there poor contact in ECM or
front oxygen (A/F) sensor con-
nector?
Repair the poor
contact in ECM or
front oxygen (A/F)
sensor connector.
Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4SO 2.0)-32,
Front Oxygen (A/
F) Sensor.>
EN(H4SO 2.0)(diag)-71
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
B: DTC P0031 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1)
DTC DETECTING CONDITION:
Immediately at fault recognition
CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:
Step
Check
Yes
No
1
CHECK ANY OTHER DTC ON DISPLAY.
Do DTC P0031 and P0037 dis-
play at the same time on the
Subaru Select Monitor?
EN-03475
3
4
1
2
5
6
B47
SBF-5
E
B47
E24
5
3
4
6
2
1
C34
C35
C33
B3
B2
B1
B135
E
B5
B6
52
B21
E2
B21
E2
50
51
3
4
E2
B21
E
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
E24
ECM
BATTERY
FRONT OXYGEN
(A/F) SENSOR
MAIN RELAY
B136
B:
C:
1
2
3
4
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
B:
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
C:
E24
3
2
*
1
*
*
3
LHD : 4
RHD : 1
*
1
*
*
2
3
3
1
6 5 4
2
: RHD
: LHD
LHD : 1
RHD : 4
LHD : 2
RHD : 6
EN(H4SO 2.0)(diag)-72
ENGINE (DIAGNOSTICS)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
2
CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen
(A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between front oxygen
(A/F) sensor connector and engine ground.
Connector & terminal
LHD model
(E24) No. 4 (+) — Engine ground (
−
):
RHD model
(E24) No. 1 (+) — Engine ground (
−
):
Is the voltage more than 10 V? Go to step 3.
Repair the power
supply line.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
main relay and
front oxygen (A/F)
sensor connector
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
main relay connec-
tor
3
CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B135) No. 5 — Chassis ground:
(B135) No. 6 — Chassis ground:
Is the resistance less than 5
Ω?
Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground terminal
• Poor contact in
ECM connector
• Poor contact in
coupling connector
4
CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of front oxygen (A/F) sensor
heater current 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 2.0)(diag)-25, Subaru Select
Monitor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual.
Is the current more than 0.2 A? Repair the poor
contact in connec-
tor.
NOTE:
In this case, repair
the following item:
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector
5
CHECK INPUT SIGNAL OF ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
−
):
(B135) No. 3 (+) — Chassis ground (
−
):
Is the voltage less than 1 V?
6
CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
−
):
(B135) No. 3 (+) — Chassis ground (
−
):
Does the voltage change by
shaking the ECM harness and
connector while monitoring the
value of voltage meter?
Repair the poor
contact in ECM
connector.
Step
Check
Yes
No
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