Subaru 2009 IMPREZA Service Manual page 563

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK FRONT OXYGEN (A/F) SENSOR
CONNECTOR AND COUPLING CONNEC-
TOR.
2 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
front oxygen (A/F) sensor connector.
3) Measure the resistance between ECM and
chassis ground.
Connector & terminal
(B135) No. 9 — Chassis ground:
(B135) No. 8 — Chassis ground:
3 CHECK POOR CONTACT.
Check for poor contact of the front oxygen (A/F)
sensor connector.
Check
Has water entered the connec-
tor?
Is the resistance 1 M or
more?
Is there poor contact of front
oxygen (A/F) sensor connec-
tor?
EN(H4SO)(diag)-146
Yes No
Completely Go to step 2.
remove any water
inside.
Go to step 3. Repair the ground
short circuit of har-
ness between
ECM and front oxy-
gen (A/F) sensor
connector.
Repair the poor Replace the front
contact of front oxygen (A/F) sen-
oxygen (A/F) sen- sor. <Ref. to
sor connector. FU(H4SO)-41,
Front Oxygen (A/F)
Sensor.>