2004 SUBARU FORESTER check engine

EN(H4SO)-111
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
P0122 or P0123
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
inspect DTC
P0121.Replace the throt-
tle position sen-
sor. FU(H4SO)-29,
Throttle Position
Sensor.>

EN(H4SO)-113
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of throttle position sensor
signal using Subaru Select Monitor or OBD-II
general scan tool.
N
OTE:
 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 less than 0.1 V? Go to step 2.Even if the mal-
function indicator
light illuminates,
the circuit has
returned to a nor-
mal condition at
this time. A tempo-
rary poor contact
of the connector
may be the cause.
N
OTE:
In this case repair
the following:
 Poor contact in
throttle position
sensor connector
 Poor contact in
ECM connector.
 Poor contact in
coupling connector
2 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground while throttle valve is fully
closed.
Connector & terminal
(B135) No. 3 (+) — Chassis ground (
−):Is the voltage more than 4.5 V? Go to step 4.Go to step 3.
3 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 3 (+) — Chassis ground (
−):Is the voltage more than 4.5 V
by shaking the ECM harness
and connector?Repair the poor
contact in ECM
connector.Contact the SUB-
ARU dealer.
N
OTE:
Inspection by DTM
is required, because
probable cause is
deterioration of mul-
tiple parts.
4 CHECK INPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 13 (+) — Chassis ground (
−):Is the voltage less than 0.1 V? Go to step 6.Go to step 5.
5 CHECK INPUT SIGNAL FOR ECM (WITH
SUBARU SELECT MONITOR).
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 13 (+) — Chassis ground (
−):Is the voltage more than 0.1 V
by shaking the ECM harness
and connector?Repair the poor
contact in ECM
connector.Go to step 6.

EN(H4SO)-114
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
6 CHECK HARNESS BETWEEN ECM AND
THROTTLE POSITION SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from throttle
position sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between throttle posi-
tion sensor connector and engine ground.
Connector & terminal
(E13) No. 4 (+) — Engine ground (
−):Is the voltage more than 4.5 V? Go to step 7.Repair harness
and connector.
N
OTE:
In this case repair
the following:
 Open circuit in
harness between
throttle position
sensor and ECM
connector
 Poor contact in
throttle position
sensor connector
 Poor contact in
ECM connector.
 Poor contact in
coupling connector
 Poor contact in
joint connector
7 CHECK HARNESS BETWEEN ECM AND
THROTTLE POSITION SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness
between ECM connector and throttle position
sensor connector.
Connector & terminal
(B135) No. 13 — (E13) No. 3:Is the resistance less than 1
Ω?Go to step 8.Repair harness
and connector.
N
OTE:
In this case repair
the following:
 Open circuit in
harness between
throttle position
sensor and ECM
connector
 Poor contact in
ECM connector.
 Poor contact in
throttle position
sensor connector
 Poor contact in
coupling connector
8 CHECK HARNESS BETWEEN ECM AND
THROTTLE POSITION SENSOR CONNEC-
TOR.
Measure the resistance of harness between
throttle position sensor connector and engine
ground.
Connector & terminal
(E13) No. 3 — Engine ground:Is the resistance more than 1
MΩ?Go to step 9.Repair ground
short circuit in har-
ness between
throttle position
sensor and ECM
connector.
9 CHECK POOR CONTACT.
Check poor contact in throttle position sensor
connector.Is there poor contact in throttle
position sensor?Repair poor con-
tact in throttle posi-
tion sensor
connector.Replace the throt-
tle position sen-
sor. FU(H4SO)-29,
Throttle Position
Sensor.> Step Check Yes No

EN(H4SO)-116
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of throttle position sensor
signal using Subaru Select Monitor or OBD-II
general scan tool.
N
OTE:
 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 more than 4.9 V? Go to step 2.Even if the mal-
function indicator
light illuminates,
the circuit has
returned to a nor-
mal condition at
this time. A tempo-
rary poor contact
of the connector
may be the cause.
N
OTE:
In this case repair
the following:
 Poor contact in
throttle position
sensor connector
 Poor contact in
ECM connector.
 Poor contact in
coupling connector
2 CHECK HARNESS BETWEEN THROTTLE
POSITION SENSOR AND ECM CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from throttle
position sensor.
3) Measure the resistance of harness
between throttle position sensor connector and
engine ground.
Connector & terminal
(E13) No. 2 — Engine ground:Is the resistance less than 5
Ω?Go to step 3.Repair harness
and connector.
NOTE:
In this case repair
the following:
 Open circuit in
harness between
throttle position
sensor and ECM
connector
 Poor contact in
coupling connector
 Poor contact in
joint connector
3 CHECK HARNESS BETWEEN THROTTLE
POSITION SENSOR AND ECM CONNEC-
TOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between throttle posi-
tion sensor connector and engine ground.
Connector & terminal
(E13) No. 3 (+) — Engine ground (
−):Is the voltage more than 4.9 V? Repair the battery
short circuit in har-
ness between
throttle position
sensor and ECM
connector. After
repair, replace the
ECM. FU(H4SO)-44,
Engine Control
Module (ECM).>Replace the throt-
tle position sen-
sor. FU(H4SO)-29,
Throttle Position
Sensor.>

EN(H4SO)-118
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 P0125.Go to step 2.
2 CHECK THERMOSTAT.Does the thermostat remain
opened?Replace the ther-
mostat. CO(H4SO)-26,
Thermostat.>Replace the
engine coolant
temperature sen-
sor. FU(H4SO)-25,
Engine Coolant
Temperature Sen-
sor.>

EN(H4SO)-119
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
R: DTC P0129 BAROMETRIC PRESSURE TOO LOW
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.>.
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 P0129.Replace the ECM.
FU(H4SO)-44,
Engine Control
Module (ECM).>

EN(H4SO)-121
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 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.
1) Race the engine at speeds from idling to
5,000 rpm for a total of 5 cycles.
2) Read the data of front oxygen (A/F) sensor
signal at racing using Subaru Select Monitor or
OBD-II general scan tool.
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)-122
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