2004 SUBARU FORESTER check engine

EN(H4SO)-124
ENGINE (DIAGNOSTIC)
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) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
front oxygen (A/F) sensor connector.
3) Measure the resistance of harness
between ECM and chassis ground.
Connector & terminal
(B136) No. 13 — Chassis ground:
(B136) No. 22 — Chassis ground:Is the resistance more than 1
MΩ?Replace the front
oxygen (A/F) sen-
sor. FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.>Repair ground
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.

EN(H4SO)-126
ENGINE (DIAGNOSTIC)
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) Turn the ignition switch to ON.
2) Disconnect the connector from front oxygen
(A/F) sensor.
3) Measure the voltage of harness between
ECM connector and chassis ground.
Connector & terminal
(B136) No. 13 (+) — Chassis ground (
−):
(B136) No. 22 (+) — Chassis ground (
−):Is the voltage more than 8 V? Replace the front
oxygen (A/F) sen-
sor. FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.>Repair battery
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.

EN(H4SO)-128
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 P0133.Go to step 2.
2 CHECK EXHAUST SYSTEM.
N
OTE:
Check the following items:
 Loose installation of front portion of exhaust
pipe onto cylinder heads
 Loose connection between front exhaust
pipe and front catalytic converter
 Damage of exhaust pipe resulting in a holeIs there a fault in exhaust sys-
tem?Repair exhaust
system.Replace the front
oxygen (A/F) sen-
sor. FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.>

EN(H4SO)-130
ENGINE (DIAGNOSTIC)
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) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
front oxygen (A/F) sensor connector.
3) Measure the resistance of harness
between ECM and front oxygen (A/F) sensor
connector.
Connector & terminal
(B136) No. 13 — (E18) No. 1:
(B136) No. 22 — (E18) No. 2:Is the resistance less than 1
Ω?Go to step 2.Repair harness
and connector.
N
OTE:
In this case repair
the following:
 Open circuit in
harness between
ECM and front
oxygen (A/F) sen-
sor connector
 Poor contact in
front oxygen (A/F)
sensor connector
 Poor contact in
ECM connector.
2 CHECK POOR CONTACT.
Check poor contact in front oxygen (A/F) sen-
sor connector. Is there poor contact in front
oxygen (A/F) sensor connec-
tor? Repair the poor
contact in front
oxygen (A/F) sen-
sor connector.Replace the front
oxygen (A/F) sen-
sor. FU(H4SO)-40,
Front Oxygen (A/
F) Sensor.>

EN(H4SO)-132
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 P0137.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 keep
the engine speed at 5,000 rpm.
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or the 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.Is the voltage more than 490
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)-133
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)-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