Subaru IMPREZA GD 2007 Series Manual page 194

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Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen
(A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between front oxygen
(A/F) sensor connector and engine ground.
Connector & terminal
(E118) No. 6 (+) — engine ground (–):
2 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the ECM.
3) Measure the resistance between ECM and
front oxygen (A/F) sensor connector.
Connector & terminal
(B136) No. 2 — (E118) No. 4:
(B136) No. 3 — (E118) No. 4:
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 FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between front oxygen
(A/F) sensor connector terminals.
Terminals
No. 6 — No. 4:
Check
Is the voltage 10 V or more?
Is the resistance less than 1 Ω? Go to step 3.
Is the resistance less than 5 Ω? Go to step 4.
Is the resistance between 2 —
3 Ω?
EN(H4SO)(diag)-85
ENGINE (DIAGNOSTICS)
Yes No
Go to step 2. Repair the power
supply line or
replace the main
relay.
NOTE:
In this case, repair
the following item:
• Open circuit of
the harness be-
tween A/F oxygen
sensor relay and
front oxygen (A/F)
sensor
• Poor contact of
A/F & oxygen sen-
sor relay connector
• Poor contact in
coupling connector
Repair the open
circuit of harness
between ECM and
front oxygen (A/F)
sensor.
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground
• Poor contact in
ECM connector
• Poor contact of
coupling connector
Repair poor con- Replace the front
tact of the ECM oxygen (A/F) sen-
connector. sor. <Ref. to
FU(H4SO)-36,
Front Oxygen (A/F)
Sensor.>