Subaru Legacy III (2000-2003 year). Service manual — part 342
EN(H6DO)-170
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Z: DTC P0138 — O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2) —
• DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)-54, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)-47, OPERATION, Inspec-
tion Mode.>.
• WIRING DIAGRAM:
EN-01088
BATTERY
F44
B61
6
T5
B19
B47
MAIN RELAY
2
1
3
5
4
6
F44
1 2 3 4
5 6 7 8
C13
B17
B19
B26
D21
D31
D9
D8
REAR
OXYGEN
SENSOR
5
3
6
4
1
3
4
2
1
5
B252
B83
B19
T5
T6
E49
B47
T6
B136
C:
D:
B135
B:
3
4
5
6
1
2
5
7
ECM
B135
B:
B136
C:
B137
D:
3
4
1
2
1 2
7
8 9
5
6
3
4
10 11 12
19 20 21
13 14 15 16
17 18
22 23 24
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
B137
1
2
7
8
9
5
6
3
4
10 11 12
19 20 21
29 30 31
13 14 15 16 17
27 28
18
22 23 24 25 26
RHD
LHD
LHD
RHD
B252
1 2 3 4
5 6 7 8
B19
4
1 2 3
6
5
2
B83
1 2 3 4
5 6 7 8 9 10
11 12
19
20
13 14 15 16 17 18
EN(H6DO)-171
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
Value
Yes
No
1
CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC is displayed?
Another DTC is displayed.
Check the relevant
DTC using “List of
Diagnostic Trou-
ble Code (DTC)”.
<Ref. to
EN(H6DO)-89, List
of Diagnostic
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 rpm to
3,000 rpm for two minutes.
2) Read data of rear oxygen sensor signal
using Subaru Select Monitor or OBD-II gen-
eral scan tool.
Does the value fluctuate?
NOTE:
• Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. <Ref. to EN(H6DO)-34,
Subaru Select Monitor.>
• OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
Value fluctuates.
3
CHECK REAR OXYGEN SENSOR DATA.
Read data of rear oxygen sensor signal using
Subaru Select Monitor or OBD-II General Scan
Tool.
Is the measured value within the specified
range?
Output maximum value 0.49 V
or more and output minimum
value 0.25 V or less.
Replace rear oxy-
gen sensor. <Ref.
to FU(H6DO)-45,
Rear Oxygen Sen-
sor.>
4
CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from ECM and rear
oxygen sensor.
3) Measure resistance of harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 19 — (T6) No. 4:
Does the measured value exceed the spec-
ified value?
3
Ω
Repair open circuit
in harness
between ECM and
rear oxygen sen-
sor connector.
5
CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from rear oxygen
sensor.
3) Turn ignition switch to ON.
4) Measure voltage between rear oxygen sen-
sor harness connector and engine ground
or chassis ground.
Connector & terminal
(T6) No. 3 (+) — Engine ground (
−−−−
):
Does the measured value exceed the spec-
ified value?
0.2 V
Replace rear oxy-
gen sensor. <Ref.
to FU(H6DO)-45,
Rear Oxygen Sen-
sor.>
Repair harness
and connector.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
ECM connector
EN(H6DO)-172
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
6
CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Loose installation of portions
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between
front oxygen (A/F) sensor and rear oxygen
sensor
Is there a fault in exhaust system?
There is a trouble.
Repair or replace
faulty parts.
Replace rear oxy-
gen sensor. <Ref.
to FU(H6DO)-45,
Rear Oxygen Sen-
sor.>
Step
Value
Yes
No
EN(H6DO)-173
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
MEMO:
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