Subaru Forester 2004 Service Manual page 82

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 connector.
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.
NOTE:
• Subaru Select Monitor
For detailed operation procedure, refer to "READ
CURRENT DATA SHOWN ON DISPLAY FOR
ENGINE". <Ref. to EN(H4DOTC 2.5)-27, Sub-
aru Select Monitor.>
• OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.
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 (
3 CHECK INPUT SIGNAL FOR ECM (WITH
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 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 connector.
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 5 V?
−
):
Is the resistance less than 1 Ω? Go to step 6.
EN(H4DOTC 2.5)-81
ENGINE (DIAGNOSTIC)
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
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 3.
Repair the poor Contact the SUB-
contact in ECM ARU dealer.
connector.
NOTE:
Inspection by DTM
is required, because
probable cause is
deterioration of mul-
tiple parts.
Go to step 5. Repair open circuit
between mass air
flow sensor and
main relay
Repair open circuit
between ECM and
mass air flow sen-
sor connector.
No