Subaru Legacy 2005 Service Manual page 1317

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 READ DATA CONNECTING SUBARU SE-
LECT MONITOR.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor or gen-
eral scan tool to data link connector.
3) Turn the ignition switch to ON and the Sub-
aru Select Monitor power switch to ON.
4) Start and idle the engine.
5) Read the voltage of mass air flow sensor
using Subaru Select Monitor or general scan
tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedure, refer to
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4DOTC)(diag)-24, Subaru Select Mon-
itor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual.
2 CHECK INPUT SIGNAL OF ECM.
Measure the voltage between ECM connector
and chassis ground while engine is idling.
Connector & terminal
(B136) No. 23 (+) — Chassis ground (
3 CHECK INPUT SIGNAL OF ECM (USING
SUBARU SELECT MONITOR).
Measure the voltage between ECM connector
and chassis ground while engine is idling.
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 the voltage between mass air flow
sensor connector and chassis ground.
Connector & terminal
(B3) No. 1 (+) — Chassis ground (
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:
(B136) No. 35 — (B3) No. 5:
Check
Is the voltage 0.2 — 4.7 V?
Is the voltage more than 0.2 V? Go to step 4.
−
):
Does the voltage change by
shaking the harness and con-
nector of ECM while monitor-
ing the value with Subaru
Select Monitor?
Is the voltage more than 10 V? Go to step 5.
−
):
Is the resistance less than 1
Ω?
EN(H4DOTC)(diag)-77
ENGINE (DIAGNOSTICS)
Yes
Even if the mal- Go to step 2.
function indicator
light illuminates,
the circuit has
returned to a nor-
mal condition at
this time. A tempo-
rary poor contact
in connector or
harness may be
the cause. Repair
the harness or
connector in mass
air flow sensor.
NOTE:
In this case, repair
the following:
• Open or ground
short circuit of har-
ness between
mass air flow sen-
sor and ECM con-
nector
• Poor contact in
mass air flow sen-
sor or ECM con-
nector
Go to step 3.
Repair the poor Replace and
contact in ECM check it again
connector. because of ECM
malfunction possi-
bility.
Repair the open
circuit between
mass air flow sen-
sor and main relay.
Go to step 6. Repair the open
circuit between
ECM and mass air
flow sensor con-
nector.
No