oxygen SUBARU FORESTER 2004 Service Workshop Manual

EN(H4SO)-135
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK ANY OTHER DTC ON DISPLAY.Is any other DTC displayed? Inspect the DTC
using “List of Diag-
nostic Trouble
Code (DTC)”.
EN(H4SO)-72, List
of Diagnostic Trou-
ble Code (DTC).>
N
OTE:
In this case, it is not
necessary to in-
spect DTC P0138.Go to step 2.
2 CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant
temperature is above 70°C (158°F), and lower
the engine speed rapidly from 5,000 rpm.
2) Read the data of rear oxygen (A/F) sensor
signal using Subaru Select Monitor or OBD-II
scan tool.
NOTE:
 Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”. to EN(H4SO)-29, Subaru Select Monitor.>
 OBD-II scan tool
For detailed operation procedures, refer to the
OBD-II Scan Tool Instruction Manual.Does the voltage vary from 250
mV?Go to step 5.Go to step 3.
3 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 in harness
between ECM and rear oxygen sensor con-
nector.
Connector & terminal
(B135) No. 14 — (T6) No. 4:
(B135) No. 19 — (T6) No. 3:Is the resistance more than 3
Ω?Repair open circuit
in harness
between ECM and
rear oxygen sen-
sor connector.Go to step 4.
4 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 0.2 — 0.5 V? Replace the rear
oxygen sensor.
FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.>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(H4SO)-136
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
5 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
N
OTE:
Check the following items:
 Loose part of exhaust system and incom-
plete installation
 Damage (crack, hole etc.) of parts
 Looseness and ill fitting of parts between
front oxygen (A/F) sensor and rear oxygen
sensorIs there a fault in exhaust sys-
tem?Repair or replace
the faulty par t.Replace the rear
oxygen sensor.
FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.> Step Check Yes No

EN(H4SO)-137
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Z: DTC P0139 O2 SENSOR CIRCUIT SLOW RESPONSE (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 ERATION, Clear Memory Mode.> and Inspection Mode tion Mode.>.
WIRING DIAGRAM:
EN-02385
BATTERYB61F44
7
B47 MAIN RELAY
12
35
46
B61
12345678
C4B14B19D15
C16C5
REAR
OXYGEN SENSOR
ECM
1432
8B21
B122
T6
E2
B47
T6B21
12 34
56 78
9
10 11 12
13 14 15 16
3456
12
1
B135 B:
D:
B137
SBF-5
C:B136
B122 : LHDB122 : RHDB137
4
1
53
2618 15 167891011
17 19
20121314
B135
567
82
94
310
24 22 23 251112131415
26 27
281617181920 21
B136
5
2
84
3923 20 211011
221617
24
2512136
261915
14
1
7
18
LHD
LHD
RHD
RHD1 8
4
143
T5
B19
2
B19T5
B122
T5
34
12
LHDLHD
RHDRHD
1234
123456781234
B:
D:C:

EN(H4SO)-138
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
AA:DTC P0171 SYSTEM TOO LEAN (BANK 1)
Refer to DTC P0172 for diagnostic procedure. (BANK 1), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
Step Check Yes No
1 CHECK ANY OTHER DTC ON DISPLAY.Is any other DTC displayed? Inspect the DTC
using “List of Diag-
nostic Trouble
Code (DTC)”.
EN(H4SO)-72, List
of Diagnostic Trou-
ble Code (DTC).>
N
OTE:
In this case, it is not
necessary to in-
spect DTC P0139.Replace the rear
oxygen sensor.
FU(H4SO)-42,
Rear Oxygen Sen-
sor.>

EN(H4SO)-164
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
AN:DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK
1)
DTC DETECTING CONDITION:
Two consecutive driving cycles with fault
TROUBLE SYMPTOM:
 Engine stalls
 Idle mixture is out of specifications.
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode ERATION, Clear Memory Mode.> and Inspection Mode tion Mode.>.
WIRING DIAGRAM:
EN-02391
B18
T6
3412
56
B47F44
12345678
T5B136
B137 B135
BATTERY
REAR
OXYGEN
SENSORFRONT OXYGEN
(A/F) SENSORMAIN RELAYSBF-5
B61 F44
B47
T6
T5
B19B18 1 2 3 5 6
4
E
7
B122
B19B14D15C43
4
2B23C13C22C6C17
1
8
1
B135ECM
B136 B :
C :
B137 D :
5
2
84
3923 20 211011
221617
24
2512136
261915
14
1
7
18
4
1
53
2618 15 167891011
17 19
20121314
567
82 1
94
310
24 22 23 251112131415
26 27
281617181920 21
LHD
LHD
RHD
RHD
4
1
B122
LHDLHD
RHDRHD
4
1 23
3
4
21
1234
3412
B122 : LHD
B122 : RHD
123456781234
B :C :
D :

EN(H4SO)-165
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK ANY OTHER DTC ON DISPLAY.Is any other DTC displayed? Inspect the rele-
vant DTC using
“List of Diagnostic
Trouble Code
(DTC)”. EN(H4SO)-72, List
of Diagnostic Trou-
ble Code (DTC).>
N
OTE:
In this case, it is not
necessary to in-
spect DTC P0420.Go to step 2.
2 CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by
loose or dislocated nuts and bolts, and open
hole at exhaust pipes.
NOTE:
Check the following positions.
 Between cylinder head and front exhaust
pipe
 Between front exhaust pipe and front cata-
lytic converter
 Between front catalytic converter and rear
catalytic converterIs there a fault in exhaust sys-
tem?Repair or replace
the exhaust sys-
tem. EX(H4SO)-2, Gen-
eral Description.>Go to step 3.
3 CHECK CATALYTIC CONVERTER.Is there damage at rear face or
front face of catalytic con-
ver ter?Replace catalytic
converter. EC(H4SO)-3,
Front Catalytic
Converter.>Go to step 4.
4 CHECK REAR OXYGEN SENSOR CIRCUIT
MALFUNCTION.
1) Disconnect the connector from rear oxygen
sensor and ECM.
2) Measure the resistance between rear oxy-
gen sensor connector and ECM connector.
Connector & terminal
(T6) No. 3 — (B135) No. 19:Is the resistance less than 1
Ω?Go to step 5.Repair battery
open circuit in har-
ness between
ECM and rear oxy-
gen sensor.
5 CHECK SHIELD WIRE.Is the shield wire opened? Repair the shield
wire.Contact the SUB-
ARU dealer.

EN(H4SO)-227
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
BT:DTC P1134 A/F SENSOR MICRO-COMPUTER PROBLEM
DTC DETECTING CONDITION:
Immediately at fault recognition
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode ERATION, Clear Memory Mode.> and Inspection Mode tion Mode.>.
WIRING DIAGRAM:
EN-02384
B18
3412
56
B47F44
12345678
B136B135
1234
B21
123
4
56
78
9
1011 12
1314 15 16
SBF-5
EE
B47
B18
6
4
5
3
2
1
B23 C13
C22C6 C17
C16
C5
8
B:
C:B135
B136
B21
E2 ECMBATTERY
B61F44
7
FRONT OXYGEN
(A/F) SENSOR MAIN RELAY
567
82 1
94
310
24
22 23251112131415
26 27
281617181920 21
5
2
84
3923 20 211011
221617
24
2512136
261915
14
1
7
18
LHDLHD
RHDRHD
4
3
1 2
B: C:

EN(H4SO)-229
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
BU:DTC P1137 O2 SENSOR CIRCUIT (LAMBDA=1) (BANK 1 SENSOR 1)
DTC DETECTING CONDITION:
Immediately at fault recognition
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode ERATION, Clear Memory Mode.> and Inspection Mode tion Mode.>.
WIRING DIAGRAM:
EN-02384
B18
3412
56
B47F44
12345678
B136B135
1234
B21
123
4
56
78
9
1011 12
1314 15 16
SBF-5
EE
B47
B18
6
4
5
3
2
1
B23 C13
C22C6 C17
C16
C5
8
B:
C:B135
B136
B21
E2 ECMBATTERY
B61F44
7
FRONT OXYGEN
(A/F) SENSOR MAIN RELAY
567
82 1
94
310
24
22 23251112131415
26 27
281617181920 21
5
2
84
3923 20 211011
221617
24
2512136
261915
14
1
7
18
LHDLHD
RHDRHD
4
3
1 2
B: C:

EN(H4SO)-230
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK ANY OTHER DTC ON DISPLAY.Is any other DTC displayed? Inspect the DTC
using “List of Diag-
nostic Trouble
Code (DTC)”.
EN(H4SO)-72, List
of Diagnostic Trou-
ble Code (DTC).>Go to step 2.
2 CHECK FRONT (A/F) OXYGEN SENSOR DA-
TA.
1) Start the engine.
2) While observing the Subaru Select Monitor
or OBD-II general scan tool screen, warm-up
the engine until coolant temperature is above
70°C (160°F).
If the engine is already warmed-up, operate at
idle speed for at least 1 minute.
3) Read the data of front oxygen (A/F) sensor
signal at idling using Subaru Select Monitor or
OBD-II general scan tool.
NOTE:
 Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”. to EN(H4SO)-29, Subaru Select Monitor.>
 OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.Is the voltage 0.85 — 1.15 V? Go to step 3.Go to step 4.
3 CHECK FRONT (A/F) OXYGEN SENSOR DA-
TA.
Race the engine at speeds from idling to 5,000
rpm for a total of 5 cycles.
N
OTE:
 Normally the air fuel ratio be rich at racing.
 To increase engine speed to 5,000 rpm,
slowly depress accelerator pedal, taking
approximately 5 seconds, and quickly release
accelerator pedal to decrease engine speed.Is the voltage more than 1.1 V? Go to step 6.Go to step 4.
4 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
front oxygen (A/F) sensor connector.
3) Measure the resistance between ECM and
front oxygen (A/F) sensor.
Connector & terminal
(B136) No. 13 — (B18) No. 1:
(B136) No. 22 — (B18) No. 2:Is the resistance less than 5
Ω?Go to step 5.Repair open circuit
between ECM and
front oxygen (A/F)
sensor.
5 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between ECM and
chassis ground.
Connector & terminal
(B136) No. 13 — Chassis ground:
(B136) No. 22 — Chassis ground:Is the resistance more than 1
MΩ?Go to step 6.Repair ground
short circuit
between ECM and
front oxygen (A/F)
sensor.

EN(H4SO)-231
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
6 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
N
OTE:
Check the following items:
 Loose installation of portions
 Damage (crack, hole etc.) of parts
 Looseness of front oxygen (A/F) sensor
 Looseness and ill fitting of parts between
front oxygen (A/F) sensor and rear oxygen
sensorIs there a fault in exhaust sys-
tem?Repair or replace
the faulty par t.Replace the front
oxygen (A/F) sen-
sor. FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.> Step Check Yes No