Subaru 2009 IMPREZA Service Manual page 549

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of intake air temperature sen-
sor signal using Subaru Select Monitor or gen-
eral 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 POOR CONTACT.
Check for poor contact of ECM and mass air
flow and intake air temperature sensor connec-
tor.
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 connector from ECM and
the mass air flow and intake air temperature
sensor.
3) Measure the resistance of harness between
ECM and the mass air flow and intake air tem-
perature sensor connector.
Connector & terminal
(B135) No. 18 — (B3) No. 1:
(B135) No. 30 — (B3) No. 2:
4 CHECK HARNESS BETWEEN ECM AND
MASS AIR FLOW AND INTAKE AIR TEM-
PERATURE SENSOR CONNECTOR.
1) Connect all connectors.
2) Turn the ignition switch to ON.
3) Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B135) No. 18 (+) — Chassis ground (–):
Check
Is the intake air temperature
less than –40°C (–40°F) ?
Is there poor contact of ECM or
mass air flow and intake air
temperature sensor connector?
Is the resistance less than 1 ? Go to step 4.
Is the voltage 5 V or more?
EN(H4SO)(diag)-132
Yes No
Go to step 2. 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.
Repair the poor Go to step 3.
contact of ECM or
mass air flow and
intake air tempera-
ture sensor con-
nector.
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and mass air
flow and intake air
temperature sen-
sor connector
• Poor contact of
joint connector
Repair the short Replace the mass
circuit of harness air flow and intake
to power supply air temperature
between ECM and sensor. <Ref. to
mass air flow and FU(H4SO)-34,
intake air tempera- Mass Air Flow and
ture sensor con- Intake Air Temper-
nector. ature Sensor.>