Subaru 2009 IMPREZA Service Manual page 1317

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Start and warm up the engine.
2) Turn the ignition switch to OFF.
3) Disconnect the connectors from ECM and
front oxygen (A/F) sensor.
4) Measure the resistance of harness between
ECM and front oxygen (A/F) sensor connector.
Connector & terminal
(B136) No. 3 — (E22) No. 2:
(B136) No. 2 — (E22) No. 2:
(B135) No. 9 — (E22) No. 1:
(B135) No. 8 — (E22) No. 3:
2 CHECK FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between front oxygen
(A/F) sensor terminals.
Terminals
No. 2 — No. 4:
3 CHECK POOR CONTACT.
Check for poor contact of ECM and front oxygen
(A/F) sensor connector.
Check
Is the resistance less than 1 ? Go to step 2.
Is the resistance less than 2 —
3 ?
Is there poor contact of ECM or
front oxygen (A/F) sensor con-
nector?
EN(H4DOTC)(diag)-96
Yes No
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and front oxy-
gen (A/F) sensor
connector
• Poor contact of
coupling connector
Go to step 3. Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4DOTC)-48,
Front Oxygen (A/F)
Sensor.>
Repair the poor Replace the front
contact of ECM or oxygen (A/F) sen-
front oxygen (A/F) sor. <Ref. to
sensor connector. FU(H4DOTC)-48,
Front Oxygen (A/F)
Sensor.>