Subaru LEGACY 2004 Service Manual page 363

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
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
(E24) No. 4 (+) — Engine ground (
3 CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B135) No. 5 — Chassis ground:
(B135) No. 6 — 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.
NOTE:
For detailed operation procedure, refer to
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4SO 2.0)(diag)-25, Subaru Select Mon-
itor.>
5 CHECK INPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
(B135) No. 3 (+) — Chassis ground (
6 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
(B135) No. 3 (+) — Chassis ground (
Check
Do DTC P0031 and P0037
appear at the same time on the
Subaru Select Monitor?
Is the voltage more than 10 V? Go to step 3.
−
):
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?
−
):
−
):
Does the voltage change by
shaking the ECM harness and
connector while monitoring the
value of voltage meter?
−
):
−
):
EN(H4SO 2.0)(diag)-74
Yes
Go to step 2. Go to step 5.
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 connec-
tor
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
Go to step 5.
contact connector.
NOTE:
In this case, repair
the following:
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector
Go to step 7. Go to step 6.
Repair the poor Go to step 7.
contact in ECM
connector.
No