Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 257
EN(H4DOTC)(diag)-252
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
3
CHECK WAVEFORM DATA ON THE SUBA-
RU SELECT MONITOR (WHILE IDLING).
1) Run the engine at idle.
2) In the condition of step 1), use the Subaru
Select Monitor to read the waveform data.
• At normal condition
• At abnormal condition 1 (numerous inver-
sion)
• At abnormal condition 2 (noise input)
Is a normal waveform dis-
played?
• The waveform is
displayed at abnor-
mal condition 1: Go
to step
• The waveform is
displayed at abnor-
mal condition 2: Go
to step
4
CHECK CATALYTIC CONVERTER.
Is the catalytic converter dam-
aged?
5
CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.
Has water entered the connec-
tor?
Completely
remove any water
inside.
Step
Check
Yes
No
EN-06668
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
EN-06669
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
EN-06670
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
EN(H4DOTC)(diag)-253
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
6
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 connector and rear oxygen sensor con-
nector.
Connector & terminal
(B136) No. 20 — (T6) No. 3:
(B135) No. 30 — (T6) No. 4:
Is the resistance less than 1 Ω? Go to step
Repair the harness
and connector.
NOTE:
Repair the follow-
ing locations.
• Open circuit in
harness between
ECM
connector
and rear oxygen
sensor connector
• Poor contact of
coupling connector
7
CHECK REAR OXYGEN SENSOR SHIELD.
1) Turn the ignition switch to OFF.
2) Expose the rear oxygen sensor connector
body side harness sensor shield.
3) Measure the resistance between sensor
shield and chassis ground.
Is the resistance less than 1 Ω? Go to step
Repair the open
circuit of rear oxy-
gen sensor har-
ness.
8
CHECK ENGINE OIL AMOUNT AND EX-
HAUST GAS.
1) Check the engine oil amount. <Ref. to
LU(STI)-11, INSPECTION, Engine Oil.>
2) Check exhaust gas during idling.
Does the engine oil amount
drop or white smoke emit from
the muffler?
Check the engine,
and repair the
defective part.
<Ref. to ME(STI)-
107, INSPEC-
TION, Engine
Trouble in Gen-
eral.> <Ref. to
ME(w/o STI)-103,
INSPECTION,
Engine Trouble in
General.>
After repairing the
engine, replace the
catalytic con-
verter. <Ref. to
EX(STI)-8, Center
Exhaust Pipe.>
After the catalytic
converter is
replaced, perform
step 2 to check the
normal waveform
is displayed, and
then exit the proce-
dure.
9
CHECK IGNITION SYSTEM.
1) Check the spark plug. <Ref. to IG(STI)-5,
INSPECTION, Spark Plug.> <Ref. to IG(w/o
STI)-6, INSPECTION, Spark Plug.>
2) Check the status of the ignition coil connec-
tor and the spark plug terminal.
Is there any fault in the ignition
system?
After repairing the
ignition system,
replace the cata-
lytic converter.
<Ref. to EX(STI)-8,
Center Exhaust
Pipe.>
After the catalytic
converter is
replaced, perform
step 2 to check the
normal waveform
is displayed, and
then exit the proce-
dure.
Step
Check
Yes
No
EN(H4DOTC)(diag)-254
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
10
Is there any fault in the fuel sys-
tem?
After repairing the
fuel system,
replace the cata-
lytic converter.
<Ref. to EX(STI)-8,
Center Exhaust
Pipe.>
After the catalytic
converter is
replaced, perform
step 2 to check the
normal waveform
is displayed, and
then exit the proce-
dure.
11
CHECK DTC.
Is any other DTC displayed?
Check the appropri-
ate DTC using the
“List of Diagnostic
Trouble Code
(DTC)”. <Ref. to
EN(H4DOTC)(diag)
-87, List of Diagnos-
tic Trouble Code
(DTC).>
After checking the
DTC, replace the
catalytic con-
verter. <Ref. to
EX(STI)-8, Center
Exhaust Pipe.>
After the catalytic
converter is
replaced, perform
step 2 to check the
normal waveform
is displayed, and
then exit the proce-
dure.
Step
Check
Yes
No
EN(H4DOTC)(diag)-255
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
CG:DTC P0441 EVAPORATIVE EMISSION CONT. SYS. INCORRECT PURGE
FLOW
DTC DETECTING CONDITION:
• Detected when two consecutive driving cycles with fault occur.
• GENERAL DESCRIPTION <Ref. to GD(H4DOTC)-152, DTC P0441 EVAPORATIVE EMISSION CONT.
SYS. INCORRECT PURGE FLOW, Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
Improper idling
CAUTION:
After servicing or replacing faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-63,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-49, PROCE-
Step
Check
Yes
No
1
CHECK FOR ANY OTHER DTC ON DISPLAY. Is any other DTC displayed?
2
CHECK PURGE CONTROL SOLENOID
VALVE.
Operate the purge control solenoid valve using
the Subaru Select Monitor.
NOTE:
Does the purge control sole-
noid valve operate?
3
CHECK EVAPORATIVE EMISSION CON-
TROL SYSTEM LINE.
1) Turn the ignition switch to OFF.
2) Check the delivery (test) mode connector is
disconnected.
Are there holes, cracks, clog-
ging, or disconnection, miscon-
nection of hoses or pipes in
evaporative emission control
system?
Repair or replace
the hoses or pipes.
Repair the poor
contact of ECM
connector.
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