Subaru 2009 IMPREZA Service Manual page 523

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B136) No. 4 (+) — 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(H4SO)(diag)-106
Yes No
Repair the short Go to step 2.
circuit to power in
the harness
between ECM and
rear oxygen 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