Subaru Legacy 2003 Service Manual page 494

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK OUTPUT SIGNAL FROM ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 6 (+) — Chassis ground ( − − − − ):
(B136) No. 17 (+) — Chassis ground ( − − − − ):
Does the measured value exceed the spec-
ified value?
2 CHECK FRONT OXYGEN (A/F) SENSOR
HEATER CURRENT.
1) Turn ignition switch to OFF.
2) Repair battery short circuit in harness
between ECM and front oxygen (A/F) sen-
sor connector.
3) Turn ignition switch to ON.
4) Read data of front oxygen (A/F) sensor
heater current using Subaru Select Monitor
or the OBD-II general scan tool.
Does the measured value exceed the spec-
ified value?
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE".
<Ref. to EN(H4SO)-32, Subaru Select Moni-
tor.>
•OBD-II general scan tool
For detailed operation procedure, refer to the
OBD-II General Scan Tool Instruction Manual.
3 CHECK OUTPUT SIGNAL FROM ECM.
Measure voltage between ECM connector and
chassis ground.
Connector & terminal
(B136) No. 6 (+) — Chassis ground ( − − − − ):
(B136) No. 17 (+) — Chassis ground ( − − − − ):
Does the measured value exceed the specified
value by shaking harness and connector of
ECM while monitoring the value?
Value
8 V
2.3 A
8 V
EN(H4SO)-97
ENGINE (DIAGNOSTICS)
Yes
Go to step 3. Go to step 2.
Replace ECM. END
<Ref. to
FU(H4SO)-45,
Engine Control
Module.>
Repair battery END
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.
No