Subaru 2009 IMPREZA Service Manual page 1323

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK POWER SUPPLY TO REAR OXY-
GEN SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor connector and engine ground.
Connector & terminal
(T6) No. 2 (+) — Engine ground (–):
2 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM.
3) Measure the resistance between the ECM
and rear oxygen sensor connector.
Connector & terminal
(B136) No. 4 — (T6) No. 1:
3 CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness 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:
4 CHECK REAR OXYGEN SENSOR.
Measure the resistance between rear oxygen
sensor terminals.
Terminals
No. 1 — No. 2:
Check
Is the voltage 10 V or more?
Is the resistance less than 1 ? Go to step 3.
Is the resistance less than 5 ? Go to step 4.
Is the resistance 5 — 7 ?
EN(H4DOTC)(diag)-102
Yes No
Go to step 2. Repair the power
supply line.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
A/F, oxygen sen-
sor relay and rear
oxygen
connector
• Poor contact of
A/F, oxygen sen-
sor relay connector
• Poor contact of
coupling connector
• Malfunction of A/
F, oxygen sensor
relay
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
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground
• Poor contact of
ECM connector
• Poor contact of
coupling connector
Repair the poor Replace the rear
contact of ECM oxygen sensor.
connector. <Ref. to
FU(H4DOTC)-50,
Rear Oxygen Sen-
sor.>
sensor