Subaru 2009 IMPREZA Service Manual page 1321

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B136) No. 3 (+) — Chassis ground (–):
(B136) No. 2 (+) — Chassis ground (–):
2 CHECK GROUND CIRCUIT FOR ECM.
1) Disconnect the connectors from ECM.
2) Measure the resistance between ECM and
chassis ground.
Connector & terminal
(B134) No. 5 — Chassis ground:
(B137) No. 1 — Chassis ground:
(B137) No. 2 — Chassis ground:
(B137) No. 3 — Chassis ground:
(B137) No. 7 — Chassis ground:
Check
Is the voltage 10 V or more?
Is the resistance less than 5 ? Repair the poor
EN(H4DOTC)(diag)-100
Yes No
Repair the short Go to step 2.
circuit to power in
the harness
between ECM and
front oxygen (A/F)
sensor connector.
Repair the harness
contact of ECM and connector.
connector.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground
• Poor contact of
coupling connector