Subaru Impreza 2003 Service Manual page 1319

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 2,000 rpm to 3,000 rpm for
2 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(H4DOTC)-
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 REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen sensor signal
using Subaru Select Monitor or OBD-II general
scan tool.
4 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
LHD model
(B135) No. 17 — (B19) No. 3:
RHD model
(B135) No. 17 — (B19) No. 4:
5 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
LHD model
(B19) No. 3 (+) — Engine ground ( − − − − ):
RHD model
(B19) No. 4 (+) — Engine ground ( − − − − ):
Check
Is any other DTC displayed?
Does the value fluctuate?
Is the voltage 0.2 — 0.4 V?
Is the resistance more than 3
Ω?
Is the voltage more than 0.2 V? Replace the rear
EN(H4DOTC)-143
ENGINE (DIAGNOSTICS)
Yes
Using the List of Go to step 2.
Diagnostic Trou-
ble Code (DTC),
check the appro-
priate DTC. <Ref.
to EN(H4DOTC)-
75, List of Diag-
nostic Trouble
Code (DTC).>
Go to step 6. Go to step 3.
Go to step 4. Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOTC)-46,
Rear Oxygen Sen-
sor.>
Repair the open Go to step 5.
circuit in harness
between ECM and
rear oxygen sen-
sor connector.
Repair the har-
oxygen sensor. ness and connec-
<Ref. to tor.
FU(H4DOTC)-46,
NOTE:
Rear Oxygen Sen-
In this case, repair
sor.>
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
No