Subaru Impreza 2003 Service Manual page 492

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1)Start the engine and warm-up engine.
2)Turn the ignition switch to OFF.
3)Disconnect the connectors from ECM and
front oxygen (A/F) sensor.
4)Measure the resistance of harness between
ECM and front oxygen (A/F) sensor connector.
Connector & terminal
(B136) No. 6 — (B18) No. 3:
(B136) No. 17 — (B18) No. 3:
2 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance of harness between
ECM and front oxygen (A/F) sensor connector.
Connector & terminal
(B136) No. 13 — (B18) No. 1:
(B136) No. 22 — (B18) No. 2:
3 CHECK HARNESS BETWEEN MAIN RELAY
AND FRONT OXYGEN (A/F) SENSOR CON-
NECTOR.
Measure the resistance of harness between
main relay and front oxygen (A/F) sensor con-
nector.
Connector & terminal
(B47) No. 4 — (B18) No. 4:
4 CHECK FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between front oxygen
(A/F) sensor connector terminals.
Terminals
No. 3 — No. 4:
5 CHECK POOR CONTACT.
Check the poor contact in ECM and front oxy-
gen (A/F) sensor connector.
Check
Is the resistance less than 1
Ω?
Is the resistance less than 1
Ω?
Is the resistance less than 1
Ω?
Is the resistance less than 5
Ω?
Is there poor contact in ECM or
front oxygen (A/F) sensor con-
nector?
EN(H4SO)-80
Yes
Go to step 2. Repair the open
circuit in harness
between ECM and
front oxygen (A/F)
sensor connector.
Go to step 3. Repair the open
circuit in harness
between ECM and
front oxygen (A/F)
sensor connector.
Go to step 4. Repair the open
circuit in harness
between ECM and
front oxygen (A/F)
sensor connector.
Go to step 5. Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4SO)-44,
Front Oxygen (A/
F) Sensor.>
Repair the poor Replace the front
contact in ECM or oxygen (A/F) sen-
front oxygen (A/F) sor. <Ref. to
sensor connector. FU(H4SO)-44,
Front Oxygen (A/
F) Sensor.>
No