Subaru Impreza 2003 Service Manual page 1461

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ECM and
front oxygen (A/F) sensor.
3)Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B84) No. 19 — Chassis ground:
2 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B84) No. 29 — Chassis ground:
3 CHECK OUTPUT SIGNAL FOR ECM.
1)Connect the connector to ECM and front
oxygen (A/F) sensor.
2)Turn the ignition switch to ON.
3)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B84) No. 19 (+) — Chassis ground ( − − − − ):
4 CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B84) No. 19 (+) — Chassis ground ( − − − − ):
5 CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B84) No. 29 (+) — Chassis ground ( − − − − ):
6 CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B84) No. 29 (+) — Chassis ground ( − − − − ):
Check
Is the resistance more than 1
MΩ?
Is the resistance more than 1
MΩ?
Is the voltage more than 4.5 V? Go to step 4.
Is the voltage more than 10 V? Repair the battery
Is the voltage more than 4.95
V?
Is the voltage more than 10 V? Repair the battery
EN(H4DOTC)-285
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Repair the ground
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.
Go to step 3. Repair the ground
short circuit in har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.
Go to step 5.
Repair the poor
short circuit in har- contact in ECM
ness between connector.
ECM and front
oxygen (A/F) sen-
sor connector.
After repair,
replace the ECM.
<Ref. to
FU(H4DOTC)-49,
Engine Control
Module (ECM).>
Go to step 6. Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4DOTC)-44,
Front Oxygen (A/
F) Sensor.>
Repair the poor
short circuit in har- contact in ECM
ness between connector.
ECM and front
oxygen (A/F) sen-
sor connector.
After repair,
replace the ECM.
<Ref. to
FU(H4DOTC)-49,
Engine Control
Module (ECM).>
No