Subaru 2009 IMPREZA Service Manual page 575

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
rear oxygen sensor.
3) Measure the resistance of harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 4 — (E23) No. 3:
2 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
Measure the resistance between rear oxygen
sensor connector and chassis ground.
Connector & terminal
(E23) No. 3 — Chassis ground:
3 CHECK REAR OXYGEN SENSOR.
Measure the resistance between rear oxygen
sensor terminals.
Terminals
No. 3 — No. 4
Check
Is the resistance less than 1 ? Go to step 2.
Is the resistance 1 M or
more?
Is the resistance less than 1 ? Replace the rear
EN(H4SO)(diag)-158
Yes No
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector
Go to step 3. Repair the ground
short circuit of har-
ness between
ECM and rear oxy-
gen sensor con-
nector.
Even if DTC is
oxygen sensor. detected, the cir-
<Ref. to cuit has returned to
FU(H4SO)-43, a normal condition
Rear Oxygen Sen- at this time. Repro-
sor.> duce the failure,
and then perform
the diagnosis
again.
NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.