2004 SUBARU FORESTER oxygen

EN(H4DOTC 2.5)-113
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
S: 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 OPERATION, Clear Memory Mode.> and Inspection Mode Inspection Mode.>.
WIRING DIAGRAM:
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(H4DOTC 2.5)-
65, List of Diag-
nostic Trouble
Code (DTC).>Go to step 2.
EN-02360
B122 B47 1 2 3 5 4 6
E
E
B21
E23
4
1
B122
34 12
56123
4
56
78
9
1011 12
1314 15 16
: B134
: B135B21
B47 T6
: B136 T6
A6
A7B2
D25
D31
C35
C : B :
D :
4
6
B83A
B
C
B136
B137 B135 B134 A :
: B137
D
56 7
82 1
94 310
24 22 23 25 11 12 13 14 15
26 27
2816 17
18 19 20 21
33 34 29
32 30 31
56
782 1
94 310
24 22 23 2511 12 13
1415
26 27
2816
17 18 19 20 21
33 34 29
32 30
31 35
567
82 1
94 310
24 22 23 2511 12 13 14 15
26 27
2816 17 18 19
20 21
29 30 31 32 33 34 35
567
82 1
94 310
22 23 11 12 13 14 15
24 25
2616 17
18 19 20 21
27 28 29 30 31
ECM MAIN RELAYBATTERY
REAR OXYGEN
SENSOR
12345678
B18 T52
B18
T5
B18
1234
B83
1
23456
1234
3 1
4
1
2
4
3

EN(H4DOTC 2.5)-114
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with 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 the data of rear oxygen (A/F) sensor
signal using Subaru Select Monitor or OBD-II
general scan tool.
N
OTE:
 Subaru Select Monitor
For detailed operation procedure, refer to
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. 2.5)-27, Subaru Select Monitor.>
 OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.Does the value fluctuate? Go to step 6.Go to step 3.
3 CHECK REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen (A/F) sensor sig-
nal using Subaru Select Monitor or OBD-II
general scan tool.Is the voltage 0.2 — 0.4 V? Go to step 4.Replace the rear
oxygen sensor.
FU(H4DOTC 2.5)-
38, Rear Oxygen
Sensor.>
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 in harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B137) No. 25 — (T6) No. 4:Is the resistance more than 3
Ω?Repair open circuit
in harness between
ECM and rear oxy-
gen sensor connec-
tor.Go to step 5.
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.
FU(H4DOTC 2.5)-
38, Rear Oxygen
Sensor.>Repair the harness
and connector.
N
OTE:
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
6 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(H4DOTC 2.5)-
38, Rear Oxygen
Sensor.> Step Check Yes No

EN(H4DOTC 2.5)-213
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(H4DOTC 2.5)-
65, List of Diag-
nostic Trouble
Code (DTC).>
N
OTE:
In this case, it is
not necessary to
inspect DTC
P1544.Go to step 2.
2 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items:
 Loose installation of exhaust manifold
 Cracks or hole of exhaust manifold
 Loose installation of front oxygen (A/F) sen-
sorIs there a fault in exhaust sys-
tem?Repair or replace
failure, then
replace the precat-
alytic converter.Contact the SUB-
ARU dealer.
NOTE:
Inspection by DTM
is required, because
probable cause is
deterioration of mul-
tiple parts.

EN(H4DOTC 2.5)-258
ENGINE (DIAGNOSTIC)
General Diagnostic Table
19.General Diagnostic Table
A: INSPECTION
1. ENGINE
NOTE:
Malfunction of parts other than those listed is also possible. General.>
Symptom Problem parts
1. Engine stalls during idling.1) Electronic throttle control
2) Manifold absolute pressure sensor
3) Mass air flow and intake air temperature sensor
4) Ignition parts (*1)
5) Engine coolant temperature sensor (*2)
6) Crankshaft position sensor (*3)
7) Camshaft position sensor (*3)
8) Fuel injection parts (*4)
2. Rough idling1) Electronic throttle control
2) Manifold absolute pressure sensor
3) Mass air flow and intake air temperature sensor
4) Engine coolant temperature sensor (*2)
5) Ignition parts (*1)
6) Air intake system (*5)
7) Fuel injection parts (*4)
8) Crankshaft position sensor (*3)
9) Camshaft position sensor (*3)
10) Oxygen sensor
11) Fuel pump and fuel pump relay
3. Engine does not return to idle.1) Electronic throttle control
2) Engine coolant temperature sensor
3) Manifold absolute pressure sensor
4) Mass air flow sensor
4. Poor acceleration1) Manifold absolute pressure sensor
2) Mass air flow and intake air temperature sensor
3) Electronic throttle control
4) Fuel injection parts (*4)
5) Fuel pump and fuel pump relay
6) Engine coolant temperature sensor (*2)
7) Crankshaft position sensor (*3)
8) Camshaft position sensor (*3)
9) A/C switch and A/C cut relay
10) Engine torque control signal circuit
11) Ignition parts (*1)
5. Engine stalls or engine sags or hesitates at
acceleration.1) Manifold absolute pressure sensor
2) Mass air flow and intake air temperature sensor
3) Engine coolant temperature sensor (*2)
4) Crankshaft position sensor (*3)
5) Camshaft position sensor (*3)
6) Purge control solenoid valve
7) Fuel injection parts (*4)
8) Fuel pump and fuel pump relay
6. Surging1) Manifold absolute pressure sensor
2) Mass air flow and intake air temperature sensor
3) Engine coolant temperature sensor (*2)
4) Crankshaft position sensor (*3)
5) Camshaft position sensor (*3)
6) Fuel injection parts (*4)
7) Throttle position sensor
8) Fuel pump and fuel pump relay