Subaru Impreza 2003 Service Manual page 1263

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. 2 (+) — Engine ground ( − − − − ):
2 CHECK GROUND CIRCUIT OF ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B84) No. 8 — Chassis ground:
(B84) No. 9 — Chassis ground:
3 CHECK CURRENT DATA.
1)Start the engine.
2)Read the data of front oxygen (A/F) sensor
heater current using Subaru Select Monitor or
OBD-II general scan tool.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE".
<Ref. to EN(H4DOTC)-32, Subaru Select Mon-
itor.>
•OBD-II scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
4 CHECK OUTPUT SIGNAL FROM ECM.
1)Start and idle the engine.
2)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B84) No. 4 (+) — Chassis ground ( − − − − ):
5 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B84) No. 4 (+) — Chassis ground ( − − − − ):
6 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B84) No. 5 (+) — Chassis ground ( − − − − ):
Check
Is the voltage more than 10 V? Go to step 2.
Is the resistance less than 5
Ω?
Is the current more than 0.2 A? Repair the poor
Is the voltage less than 1 V?
Shake the ECM harness and
connector, while monitoring
value of voltage meter. Does
the voltage change?
Is the voltage less than 1 V?
EN(H4DOTC)-87
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 con-
nector
Go to step 3. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and engine
ground cable
• Poor contact in
ECM connector
• Poor contact in
coupling connector
Go to step 4.
contact in connec-
tor.
NOTE:
In this case, repair
the following:
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector
Go to step 6. Go to step 5.
Repair the poor Go to step 6.
contact in ECM
connector.
Go to step 8. Go to step 7.
No