Subaru 2009 IMPREZA Service Manual page 573

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant
temperature is higher than 75°C (167°F), and
rapidly reduce the engine speed from 3,000
rpm.
2) Read the data of rear oxygen sensor signal
using Subaru Select Monitor or general scan
tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedures, refer to
"READ CURRENT DATA FOR ENGINE". <Ref.
to EN(H4SO)(diag)-34, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedures, refer to the
general scan tool operation manual.
2 CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.
3 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
rear oxygen sensor.
3) Measure the resistance of harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B135) No. 4 — (E23) No. 3:
(B134) No. 29 — (E23) No. 4:
4 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR.
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 connector and chassis ground.
Connector & terminal
(E23) No. 3 (+) — Chassis ground (–):
5 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
• Looseness and improper fitting of exhaust
system parts
• Damage (crack, hole etc.) of parts
• Loose part and improper installation between
front oxygen (A/F) sensor and rear oxygen sen-
sor
Check
Is the voltage 250 mV or less? Go to step 5.
Has water entered the connec-
tor?
Is the resistance less than 1 ? Go to step 4.
Is the voltage 0.2 — 0.5 V?
Is there any fault in exhaust
system?
EN(H4SO)(diag)-156
Yes No
Go to step 2.
Completely Go to step 3.
remove any water
inside.
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector
Replace the rear Repair the harness
oxygen sensor. and connector.
<Ref. to
NOTE:
FU(H4SO)-43,
In this case, repair
Rear Oxygen Sen-
the following item:
sor.>
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
rear oxygen sen-
sor connector
• Poor contact of
ECM connector
Repair or replace Replace the rear
faulty parts. oxygen sensor.
<Ref. to
FU(H4SO)-43,
Rear Oxygen Sen-
sor.>