Subaru Impreza 2003, Service Manual

Page: 550 / 3610

EN(H4SO)-138
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step Check Yes No
1 CHECK ANY OTHER DTC ON DISPLAY. Is any other DTC displayed? Check DTC using
“List of Diagnostic
Trouble Code
(DTC)”. <Ref. to
EN(H4SO)-73, List
of Diagnostic
Trouble Code
(DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0138.
Go to step 2.
2 CHECK REAR OXYGEN SENSOR DATA.
1)Warm-up the engine until engine coolant
temperature is above 70
°
C (158
°
F), and imme-
diately decrease the engine speed from 5,000
rpm.
2)Read the data of rear oxygen sensor signal
using Subaru Select Monitor or OBD-II general
scan tool.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. <Ref. to EN(H4SO)-31,
Subaru Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
Is the voltage 250 mV? Go to step 5. Go to step 3.
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 connector.
Connector & terminal
(B135) No. 14 — (B19) No. 4:
(B135) No. 19 — (B19) No. 3:
Is the resistance more than 3
Ω
?
Repair open circuit
in harness
between ECM and
rear oxygen sen-
sor connector. Go to step 4.
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
(B19) No. 4 (+) — Engine ground (
−−−−
):
Is the voltage 0.2 — 0.5 V? Replace the rear
oxygen sensor.
<Ref. to
FU(H4SO)-44,
Front Oxygen (A/
F) Sensor.> Repair harness
and connector.
NOTE:
In this case, repair
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