Subaru 2002 IMPREZA Service Manual page 613

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK ANY OTHER DIAGNOSTIC TROU-
BLE CODE (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 REAR CATALYTIC CONVERTER.
Separate the rear catalytic converter from rear
exhaust pipe.
4 CHECK FRONT CATALYTIC CONVERTER.
Remove the front catalytic converter.
5 CHECK REAR OYXGEN SENSOR HARNESS
SHIELD.
Visually check the rear oxygen sensor harness
shield for damage or open.
6 CHECK GROUND CIRCUIT ON ECM.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ECM.
3)Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B136) No. 21 — Chassis ground:
Check
Is any other DTC displayed?
Is there a fault in exhaust sys-
tem?
Is there damage at rear face of
rear catalyst?
Is there damage at rear face or
front face of front catalyst?
Is there damage or open on
the rear oxygen sensor har-
ness shield?
Is the resistance less than 5
Ω?
EN-181
ENGINE (DIAGNOSTICS)
Yes
Inspect the rele- Go to step 2.
vant DTC using
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN-83, List of
Diagnostic Trou-
ble 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-
2, General
Description.>
Replace the front Go to step 4.
catalytic converter
<Ref. to EC-3,
Front Catalytic
Converter.> and
rear catalytic con-
verter <Ref. to EC-
6, Rear Catalytic
Converter.>.
Replace the front Go to step 5.
catalytic con-
verter. <Ref. to
EC-3, Front Cata-
lytic Converter.>
Repair the har- Go to step 6.
ness and connec-
tor
Go to step 7. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and engine
ground terminal
• Poor contact in
ECM connector
• Poor contact in
coupling connector
(B22)
No