Subaru 2002 IMPREZA Service Manual page 523

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
2 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 ( − − − − ):
3 CHECK GROUND CIRCUIT OF ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B134) No. 35 — Chassis ground:
(B134) No. 34 — Chassis ground:
4 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-34, Subaru Select Monitor.>
•OBD-II scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
5 CHECK OUTPUT SIGNAL FROM ECM.
1)Start and idle the engine.
2)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B134) No. 22 (+) — Chassis ground ( − − − − ):
6 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B134) No. 22 (+) — Chassis ground ( − − − − ):
7 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B134) No. 23 (+) — Chassis ground ( − − − − ):
Check
Is the voltage more than 10 V? Go to step 3.
Is the resistance less than 5
Ω?
Is the value more than 0.2 A?
Is the voltage less than 1.0 V? Go to step 7.
Does the voltage change less
than 1.0 V by shaking harness
and connector of ECM while
monitoring the value with volt-
age meter?
Is the voltage less than 1.0 V? Go to step 9.
EN-91
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 4. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and engine
ground terminal
• Poor contact in
ECM connector
Poor contact in
coupling connector
(B22)
Repair the poor Go to step 5.
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.
Repair the poor Go to step 7.
contact in ECM
connector.
Go to step 8.
No