Subaru Legacy 2003 Service Manual page 1950

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant
temperature is above 70°C (158°F), and
keep the engine speed at 2,000 rpm to
3,000 rpm for two minutes.
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor.
Does the value fluctuate?
NOTE:
For detailed operation procedure, refer to the
"READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE". <Ref. to EN(H4DOSTC)-
26, Subaru Select Monitor.>
2 CHECK REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen sensor signal
using Subaru Select Monitor or OBD-II Gen-
eral Scan Tool.
Is the measured value within the specified
value?
3 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and
rear oxygen sensor.
3) Measure the resistance of harness
between ECM and rear oxygen sensor con-
nector.
Connector & terminal
(B135) No. 26 — (T6) No. 4:
Does the measured value exceed the spec-
ified value?
4 CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor harness connector and engine
ground or chassis ground.
Connector & terminal
(T6) No. 4 (+) — Engine ground ( − − − − ):
Does the measured value exceed the spec-
ified value?
5 CHECK EXHAUST SYSTEM.
Check the exhaust system parts.
Is there a fault in exhaust system?
NOTE:
Check the following items.
•Loose installation of portions
•Damage (crack, hole etc.) of parts
•Looseness and ill fitting of parts between front
oxygen (A/F) sensor and rear oxygen sensor
Value
The value fluctuates.
0.2 — 0.4 V
3 Ω
0.2 V
There is a fault.
EN(H4DOSTC)-111
ENGINE (DIAGNOSTICS)
Yes
Go to step 5. Go to step 2.
Go to step 3. Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOSTC)-
39, Rear Oxygen
Sensor.>
Repair the open Go to step 4.
circuit in harness
between ECM and
rear oxygen sen-
sor connector.
Replace the rear Repair the har-
oxygen sensor. ness and connec-
<Ref. to tor.
FU(H4DOSTC)-
NOTE:
39, Rear Oxygen
In this case, repair
Sensor.>
the following:
• Open circuit in
harness between
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
ECM connector
Repair or replace Replace the rear
the faulty parts. oxygen sensor.
<Ref. to
FU(H4DOSTC)-
39, Rear Oxygen
Sensor.>
No