2004 SUBARU FORESTER check engine

EN(H4DOTC)-91
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
6 CHECK POWER SUPPLY TO REAR OXY-
GEN SENSOR.
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 connector and engine ground or chas-
sis ground.
Connector & terminal
(T6) No. 1 (+) — Chassis ground (
−):Is the voltage more than 10 V? Go to step 7.Repair the power
supply line.
N
OTE:
In this case repair
the following:
 Open circuit in
harness between
main relay and
rear oxygen sen-
sor connector
 Poor contact in
rear oxygen sen-
sor connector
 Poor contact in
coupling connector
7 CHECK REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between rear oxy-
gen sensor connector terminals.
Te r m i n a l s
No. 1 — No. 2:Is the resistance less than 30
Ω?Repair the har-
ness and connec-
tor.
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.
 Poor contact in
coupling connectorReplace the rear
oxygen sensor.
FU(H4DOTC)-47,
Rear Oxygen Sen-
sor.> Step Check Yes No

EN(H4DOTC)-93
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK INPUT SIGNAL FROM ECM.
1) Turn the ignition switch to OFF.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
−):Is the voltage more than 8 V? Go to step 2.Go to step 3.
2 CHECK CURRENT DATA.
1) Repair battery short circuit in harness
between ECM and rear oxygen sensor con-
nector.
2) Turn the ignition switch to ON.
3) Read the data of rear oxygen (A/F) sensor
heater current 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”. 33, Subaru Select Monitor.>
 OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.Is the current more than 7 A? Replace the ECM.
FU(H4DOTC)-50,
Engine Control
Module (ECM).>END.
3 CHECK POOR CONTACT.
Check poor contact in ECM connector.Is there poor contact in ECM
connector?Repair the poor
contact in ECM
connector.END.

EN(H4DOTC)-96
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK IDLE SWITCH SIGNAL.
1) Turn the ignition switch to ON.
2) Operate the LED operation mode for
engine using Subaru Select Monitor.
N
OTE:
 Subaru Select Monitor
For detailed operation procedure, refer to the
“LED OPERATION MODE FOR ENGINE”.
itor.>Does the LED of {Idle Switch
Signal} come on?Go to step 2.Check the throttle
position sensor cir-
cuit. EN(H4DOTC)-
122, DTC P0121
THROTTLE/
PEDAL POSI-
TION SENSOR/
SWITCH “A” CIR-
CUIT RANGE/
PERFORMANCE,
Diagnostic Proce-
dure with Diagnos-
tic Trouble Code
(DTC).>
N
OTE:
In this case, it is
not necessary to
inspect DTC
P0106.
2 CHECK ANY OTHER DTC ON DISPLAY.Is any other DTC displayed? Check related
DTC.“List of Diag-
nostic Trouble
Code (DTC)” to EN(H4DOTC)-
74, List of Diag-
nostic Trouble
Code (DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0106.Go to step 3.
3 CHECK MANIFOLD ABSOLUTE PRESSURE
SENSOR CONDITION.Is the manifold absolute pres-
sure sensor installation bolt
tightened securely?Go to step 4.Tighten manifold
absolute pressure
sensor installation
bolt securely.
4 CHECK CONDITION OF THROTTLE BODY.Is the throttle body installation
bolt tightened securely?Replace the mani-
fold absolute pres-
sure sensor. to FU(H4DOTC)-
36, Manifold Abso-
lute Pressure Sen-
sor.>Tighten throttle
body installation
bolt securely.

EN(H4DOTC)-98
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)-74,
List of Diagnostic
Trouble Code
(DTC).>
N
OTE:
In this case, it is
not necessary to
inspect DTC
P0101.Replace the mass
air flow and intake
air temperature
sensor. FU(H4DOTC)-35,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>

EN(H4DOTC)-100
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CONNECT SUBARU SELECT MONITOR OR
THE OBD-II GENERAL SCAN TOOL, AND
READ DATA.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or the
OBD-II general scan tool to data link connec-
tor.
3) Turn the ignition switch to ON and the Sub-
aru Select Monitor or OBD-II general scan tool
switch to ON.
4) Start the engine.
5) Connect the Subaru Select Monitor or
OBD-II general scan tool, and read the mass
air flow sensor voltage.
N
OTE:
 Subaru Select Monitor
For detailed operation procedure, refer to
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. 33, 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 0.2 — 4.7 V? 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 or
harness may be
the cause.Repair
harness or con-
nector in the mass
air flow sensor.
NOTE:
In this case repair
the following:
 Open or ground
short circuit in har-
ness between
mass air flow sen-
sor and ECM con-
nector
 Poor contact in
mass air flow sen-
sor or ECM con-
nectorGo to step 2.
2 CHECK INPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground while engine is idling.
Connector & terminal
(B136) No. 23 (+) — Chassis ground (
−):Is the voltage more than 0.2 V? Go to step 4.Go to step 3.
3 CHECK INPUT SIGNAL FOR ECM (WITH
SUBARU SELECT MONITOR).
Measure the voltage between ECM connector
and chassis ground while engine is idling.Does the voltage change by
shaking the harness and con-
nector of ECM while monitor-
ing the value with Subaru
Select Monitor?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 POWER SUPPLY TO MASS AIR
FLOW SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from mass air
flow sensor.
3) Turn the ignition switch to ON.
4) Measure voltage between mass air flow
sensor connector and chassis ground.
Connector & terminal
(B3) No. 1 (+) — Chassis ground (
−):Is the voltage more than 5 V? Go to step 5.Repair open circuit
between mass air
flow sensor and
main relay

EN(H4DOTC)-101
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
5 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM and mass air flow sensor con-
nector.
Connector & terminal
(B136) No. 23 — (B3) No. 3:
(B136) No. 31 — (B3) No. 2:
(B135) No. 35 — (B3) No. 5:Is the resistance less than 1
Ω?Go to step 6.Repair open circuit
between ECM and
mass air flow sen-
sor connector.
6 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW SENSOR CONNECTOR.
Measure the resistance of harness between
ECM and chassis ground.
Connector & terminal
(B136) No. 23 — Chassis ground:
(B136) No. 31 — Chassis ground:
(B135) No. 35 — Chassis ground:Is the resistance more than 1
MΩ?Go to step 7.Repair ground
short circuit
between ECM and
mass air flow sen-
sor connector.
7 CHECK POOR CONTACT.
Check poor contact in mass air flow sensor
connector.Is there poor contact in mass
air flow sensor connector?Repair poor con-
tact in mass air
flow sensor con-
nector.Replace the mass
air flow and intake
air temperature
sensor. FU(H4DOTC)-35,
Mass Air Flow and
Intake Air Temper-
ature Sensor.> Step Check Yes No

EN(H4DOTC)-103
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CONNECT SUBARU SELECT MONITOR OR
THE OBD-II GENERAL SCAN TOOL, AND
READ DATA.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or the
OBD-II general scan tool to data link connec-
tor.
3) Turn the ignition switch to ON and the Sub-
aru Select Monitor or OBD-II general scan tool
switch to ON.
4) Start the engine.
5) Connect the Subaru Select Monitor or
OBD-II general scan tool, and read the mass
air flow sensor voltage.
N
OTE:
 Subaru Select Monitor
For detailed operation procedure, refer to
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. 33, 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 0.2 — 4.7 V? Even if the mal-
function indicator
light illuminates,
the circuit has
returned to a nor-
mal condition at
this time.Go to step 2.
2 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from mass air-
flow sensor.
3) Turn the ignition switch to ON.
4) Measure voltage between mass air flow
sensor connector and chassis ground.
Connector & terminal
(B3) No. 3 (+) — Chassis ground (
−):Is the voltage more than 5 V? Repair battery
short circuit in har-
ness between
mass air flow sen-
sor connector and
ECM connector. Go to step 3.
3 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM connector and mass air flow
sensor connector.
Connector & terminal
(B3) No. 2 — (B136) No. 31:Is the resistance less than 1
Ω?Replace the mass
air flow sensor.
FU(H4DOTC)-35,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>Repair open circuit
in harness
between mass air
flow sensor con-
nector and ECM
connector.

EN(H4DOTC)-106
ENGINE (DIAGNOSTIC)
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step Check Yes No
1 CHECK INPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 16 (+) — Chassis ground (
−):Is the voltage more than 4.5 V? Go to step 3.Go to step 2.
2 CHECK INPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 16 (+) — Chassis ground (
−):Does the voltage change by
shaking the harness and con-
nector of ECM while monitor-
ing the value with voltage
meter?Repair the poor
contact in ECM
connector.Contact the SUB-
ARU dealer.
N
OTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.
3 CHECK INPUT SIGNAL FROM ECM.
Measure the voltage between ECM and chas-
sis ground.
Connector & terminal
(B136) No. 22 (+) — Chassis ground (
−):Is the voltage less than 0.7 V? Go to step 4.Contact the SUB-
ARU dealer.
N
OTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.
4 CHECK HARNESS BETWEEN ECM AND
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the manifold
absolute pressure sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between manifold
absolute pressure sensor connector and
engine ground.
Connector & terminal
(E21) No. 3 (+) — Engine ground (
−):Is the voltage more than 4.5 V? Go to step 5.Repair the open
circuit in harness
between ECM and
manifold absolute
pressure sensor
connector.
5 CHECK HARNESS BETWEEN ECM AND
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM and manifold absolute pressure
sensor connector.
Connector & terminal
(B136) No. 35 — (E21) No. 2:Is the resistance less than 1
Ω?Go to step 6.Repair the open
circuit in harness
between ECM and
manifold absolute
pressure sensor
connector.
6 CHECK HARNESS BETWEEN ECM AND
MANIFOLD ABSOLUTE PRESSURE SEN-
SOR CONNECTOR.
Measure the resistance of harness between
manifold absolute pressure sensor connector
and engine ground.
Connector & terminal
(E21) No. 1 — Engine ground:Is the resistance more than 1
MΩ?Go to step 7.Repair the ground
short circuit in har-
ness between
ECM and mani-
fold absolute pres-
sure sensor
connector.
7 CHECK POOR CONTACT.
Check poor contact in manifold absolute pres-
sure sensor connector.Is there poor contact in mani-
fold absolute pressure sensor
connector?Repair poor con-
tact in manifold
absolute pressure
sensor connector.Replace the mani-
fold absolute pres-
sure sensor. to FU(H4DOTC)-
36, Manifold Abso-
lute Pressure Sen-
sor.>