Subaru Legacy 2003 Service Manual page 1906

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
Does the Subaru Select Monitor or OBD-II
general scan tool indicate DTC P0031 and
P0037 at the same time?
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 ( − − − − ):
Does the measured value exceed the spec-
ified value?
3 CHECK GROUND CIRCUIT OF ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B137) No. 8 — Chassis ground:
(B137) No. 9 — Chassis ground:
Is the measured value less than the specified
value?
4 CHECK CURRENT DATA.
1) Start the engine
2) Read the data of front oxygen (A/F) sensor
heater current using Subaru Select Monitor.
Is the measured value less than the speci-
fied value?
NOTE:
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4DOSTC)-26, Subaru Select Monitor.>
5 CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B137) No. 4 (+) — Chassis ground ( − − − − ):
(B137) No. 5 (+) — Chassis ground ( − − − − ):
Is the measured value less than the speci-
fied value?
Value
Indicated.
10 V
5 Ω
0.2 A
1.0 V
EN(H4DOSTC)-67
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Go to step 5.
Go to step 3. 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 cable
• Poor contact in
ECM connector
Poor contact in
coupling connector
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 7. Go to step 6.
No