Subaru IMPREZA 2004 Service Manual page 478

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
2 CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by
loose or dislocated nuts and bolts, and open
hole at exhaust pipes.
NOTE:
Check the following positions.
•Between cylinder head and front exhaust pipe
•Between front exhaust pipe and front catalytic
converter
•Between front catalytic converter and rear cat-
alytic converter
3 CHECK CATALYTIC CONVERTER.
4 CHECK REAR OXYGEN SENSOR GROUND
HARNESS.
1)Disconnect the rear oxygen sensor and ECM
connectors.
2)Measure the resistance between rear oxy-
gen sensor connector and ECM connector.
Connector & terminal
(B19) No. 3 — (B135) No. 19:
5 CHECK SHIELD HARNESS.
Check
Is any other DTC displayed?
Is there a fault in exhaust sys-
tem?
Is there damage at rear face or
front face of front catalyst?
Is the resistance less than 1
Ω?
Is the shield harness opened? Repair the shield
EN(H4SO)(diag)-169
ENGINE (DIAGNOSTICS)
Yes
Inspect the rele- Go to step 2.
vant DTC using
"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 P0420.
Repair or replace Go to step 3.
the exhaust sys-
tem. <Ref. to
EX(H4SO)-2, Gen-
eral Description.>
Replace the cata- Go to step 4.
lytic converter.
<Ref. to
EC(H4SO)-3,
Front Catalytic
Converter.>
Go to step 5. Repair the open
circuit in harness
between ECM and
rear oxygen sen-
sor.
Contact with your
harness. Subaru distributor
service.
No