Subaru 2009 IMPREZA Service Manual page 537

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of air flow sensor signal using
Subaru Select Monitor or general scan tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedures, refer to
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4SO)(diag)-34, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.
2 CHECK POWER SUPPLY OF MASS AIR
FLOW AND INTAKE AIR TEMPERATURE
SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the mass
air flow and intake air temperature sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between mass air flow
and intake air temperature sensor connector
and engine ground.
Connector & terminal
(B3) No. 3 (+) — Engine ground (–):
3 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM.
3) Measure the resistance of harness between
ECM and the mass air flow and intake air tem-
perature sensor connector.
Connector & terminal
(B135) No. 26 — (B3) No. 5:
4 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
Measure the resistance between ECM and
chassis ground.
Connector & terminal
(B135) No. 26 — Chassis ground:
5 CHECK POOR CONTACT.
Check for poor contact of ECM and mass air
flow and intake air temperature sensor connec-
tor.
Check
Is the voltage less than 0.2 V? Go to step 2.
Is the voltage 10 V or more?
Is the resistance less than 1 ? Go to step 4.
Is the resistance 1 M or
more?
Is there poor contact of ECM or
mass air flow and intake air
temperature sensor connector?
EN(H4SO)(diag)-120
Yes No
Even if DTC is
detected, the cir-
cuit has returned to
a normal condition
at this time. Repro-
duce the failure,
and then perform
the diagnosis
again.
NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.
Go to step 3. Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
main relay
mass air flow and
intake air tempera-
ture sensor con-
nector
• Poor contact of
main relay connec-
tor
Repair the open
circuit in harness
between ECM and
the mass air flow
and intake air tem-
perature sensor
connector.
Go to step 5. Repair the short
circuit to ground in
harness between
ECM and the mass
air flow and intake
air temperature
sensor connector.
Repair the poor Replace the mass
contact of ECM or air flow and intake
mass air flow and air temperature
intake air tempera- sensor. <Ref. to
ture sensor con- FU(H4SO)-34,
nector. Mass Air Flow and
Intake Air Temper-
ature Sensor.>
and