Subaru IMPREZA 2004 Service Manual page 444

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
2 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 5,000 rpm for two minutes.
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)(diag)-32, Subaru Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
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:
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 ( − − − − ):
Check
Is any other DTC displayed?
Is the voltage 490 mV?
Is the resistance more than 3
Ω?
Is the voltage 0.2 — 0.5 V?
EN(H4SO)(diag)-135
ENGINE (DIAGNOSTICS)
Yes
Check DTC using Go to step 2.
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN(H4SO)(diag)-
74, List of Diag-
nostic Trouble
Code (DTC).>
NOTE:
In this case, it is
not necessary to
inspect
DTC P0137.
Go to step 5. Go to step 3.
Repair open circuit Go to step 4.
in harness
between ECM and
rear oxygen sen-
sor connector.
Replace the rear Repair harness
oxygen sensor. and connector.
<Ref. to
NOTE:
FU(H4SO)-43,
In this case, repair
Front Oxygen (A/
the following:
F) Sensor.>
• 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
No