Subaru Legacy 2003 Service Manual page 1998

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK OUTPUT SIGNAL FROM ECM.
1) Turn the ignition switch to ON.
2) Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B136) No. 10 (+) — Chassis ground ( − − − − ):
Does the measured value exceed the spec-
ified value?
2 CHECK POWER SUPPLY TO IDLE AIR CON-
TROL SOLENOID VALVE.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from idle air con-
trol solenoid valve.
3) Turn the ignition switch to ON.
4) Measure the voltage between idle air con-
trol solenoid valve and engine ground.
Connector & terminal
(E7) No. 2 (+) — Engine ground ( − − − − ):
Does the measured value exceed the spec-
ified value?
3 CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM and idle air control solenoid
valve connector.
Connector & terminal
(B136) No. 10 — (E7) No. 1:
Is the measured value less than the speci-
fied value?
4 CHECK HARNESS BETWEEN ECM AND
IDLE AIR CONTROL SOLENOID VALVE
CONNECTOR.
Measure the resistance of harness between
ECM and chassis ground.
Connector & terminal
(B136) No. 10 — Chassis ground:
Does the measured value exceed the specified
value?
5 CHECK GROUND CIRCUIT OF IDLE AIR
CONTROL SOLENOID VALVE.
Measure the resistance of harness between
idle air control solenoid valve connector and
engine ground.
Connector & terminal
(E7) No. 3 — Engine ground:
Is the measured value less than the specified
value?
Value
3 V
10 V
1 Ω
1 MΩ
5 Ω
EN(H4DOSTC)-159
ENGINE (DIAGNOSTICS)
Yes
Repair the poor Go to step 2.
contact in ECM
connector.
Go to step 3. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
idle air control
solenoid valve and
main relay con-
nector
• Poor contact in
coupling connector
Go to step 4. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and idle air
control solenoid
valve connector
• Poor contact in
coupling connector
Go to step 5. Repair the ground
short circuit in har-
ness between
ECM and idle air
control solenoid
valve connector.
Go to step 6. Repair the open
circuit in harness
between idle air
control solenoid
valve connector
and engine ground
cable.
No