Subaru Legacy 2003 Service Manual page 1918

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
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 con-
nector.
3) Turn the ignition switch to ON and Subaru
Select Monitor or the OBD-II general scan
tool switch to ON.
4) Start the engine and run it at idle.
5) Read the data of mass air flow sensor sig-
nal using Subaru Select Monitor.
Is the measured value within the specified
value?
NOTE:
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4DOSTC)-26, Subaru Select Monitor.>
2 CHECK INPUT SIGNAL FOR ECM.
Measure the voltage between ECM connector
and chassis ground while engine is idling.
Connector & terminal
(B84) No. 13 (+) — Chassis ground ( − − − − ):
Is the measured value less than the specified
value?
3 CHECK INPUT SIGNAL FOR ECM (USING
SUBARU SELECT MONITOR).
Measure the voltage between ECM connector
and chassis ground while engine is idling.
Does the measured value change by shaking
harness and connector of ECM while monitor-
ing the value with Subaru Select Monitor?
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 ( − − − − ):
Does the measured value exceed the spec-
ified value?
Value
1.3 g/sec (0.172 lb/min) — 240
g/sec (32 lb/min) or 0.3 — 4.58
V
0.2 V
The value changes.
10V
EN(H4DOSTC)-79
ENGINE (DIAGNOSTICS)
Yes
Even if MI lights Go to step 2.
up, 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-
nector
Go to step 4. Go to step 3.
Repair the poor Contact SUBARU
contact in ECM distributor service.
connector.
NOTE:
Inspection by DTM
is required,
cause
cause is deteriora-
tion of
parts.
Go to step 5. Repair the open
circuit between
mass air flow sen-
sor and main relay
No
be-
probable
multiple