Subaru LEGACY 2006 Manual page 124

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Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of rear oxygen (A/F) sensor
heater current using Subaru Select Monitor or
general scan tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedure, refer to
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4SO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual.
2 CHECK OUTPUT SIGNAL OF ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B136) No. 4 (+) — Chassis ground (–):
3 CHECK OUTPUT SIGNAL OF ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 4 (+) — Chassis ground (–):
4 CHECK OUTPUT SIGNAL OF ECM.
1) Disconnect the connector from the rear
oxygen sensor.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B136) No. 4 (+) — Chassis ground (–):
5 CHECK POWER SUPPLY TO REAR OXY-
GEN SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the rear
oxygen sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor connector and engine ground or chas-
sis ground.
Connector & terminal
(E23) No. 2 (+) — Chassis ground (–):
Check
Is the current more than 0.2 A? Repair the con-
Is the voltage less than 1 V?
Does the voltage change by
shaking the ECM harness and
connector?
Is the voltage less than 1 V?
Is the voltage more than 10 V? Go to step 6.
EN(H4SO)(diag)-87
ENGINE (DIAGNOSTICS)
Yes No
Go to step 2.
nector.
NOTE:
In this case, repair
the following item:
• Poor contact of
the rear oxygen
sensor connector
• Poor contact in
rear oxygen sensor
connecting harness
connector
• Poor contact in
ECM connector
Go to step 5. Go to step 3.
Repair the poor Go to step 4.
contact of ECM
connector.
Replace the ECM. Repair the battery
<Ref. to short circuit of har-
FU(H4SO)-36, ness between
Engine Control ECM and rear oxy-
Module (ECM).> gen sensor con-
nector. After
repair, replace the
ECM. <Ref. to
FU(H4SO)-36,
Engine Control
Module (ECM).>
Repair the power
supply line or
replace the main
relay.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
oxygen sensor re-
lay and rear oxygen
sensor connector
• Poor contact in
oxygen sensor re-
lay connector
• Poor contact of
coupling connector