Subaru Legacy 2004 Service Manual page 1350

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
(B18) No. 3 (+) — Engine ground (
2 CHECK HARNESS BETWEEN FRONT OXY-
GEN (A/F) SENSOR AND ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM.
3) Measure the voltage between front oxygen
(A/F) sensor connector and ECM.
Connector & terminal
(B18) No. 4 — (B134) No. 2:
(B18) No. 4 — (B134) No. 3:
3 CHECK HARNESS BETWEEN FRONT OXY-
GEN (A/F) SENSOR AND ECM.
Measure the resistance between ECM connec-
tor and chassis ground.
Connector & terminal
(B134) No. 2 — Chassis ground:
(B134) No. 3 — Chassis ground:
4 CHECK FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between front oxy-
gen (A/F) sensor connector terminals.
Terminals
No. 3 — No. 4:
Check
Is the voltage more than 10 V? Go to step 2.
"
):
Is the resistance less than 1
'?
Is the resistance more than 1
M'?
Is the resistance 2.4 '?
EN(H4DOTC)(diag)-61
ENGINE (DIAGNOSTICS)
Yes
Repair the power
supply line.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
main relay and
front oxygen (A/F)
sensor connector
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
main relay connec-
tor
Go to step 3. Repair the open
circuit in harness
between ECM and
front oxygen (A/F)
sensor.
Go to step 4. Repair the ground
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor.
Repair the poor Replace the front
contact in ECM oxygen (A/F) sen-
connector. sor. <Ref. to
FU(H4DOTC)-33,
Front Oxygen (A/
F) Sensor.>
No