Subaru 2004 LEGACY Service Manual page 133

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
BL:DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK
1)
DTC DETECTING CONDITION:
Two consecutive driving cycles with fault
TROUBLE SYMPTOM:
• Engine stalls.
• Idle mixture is out of specifications.
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)(diag)-40,
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-33, PROCEDURE,
Inspection Mode.>.
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 cata-
lytic converter
• Between front catalytic converter and rear
catalytic converter
3 CHECK REAR CATALYTIC CONVERTER.
Separate the rear catalytic converter from rear
exhaust pipe.
4 CHECK FRONT CATALYTIC CONVERTER.
Separate the front catalytic converter.
Check
Is any other DTC displayed?
Is there any fault in exhaust
system?
Is there damage at rear face of
rear catalyst?
Is there damage at rear face or
front face of front catalyst?
EN(H6DO)(diag)-202
Yes
Inspect the rele- Go to step 2.
vant DTC using
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN(H6DO)(diag)-
66, 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.
Front catalytic con- Go to step 4.
verter <Ref. to
EC(H6DO)-3,
Front Catalytic
Converter.> and
rear catalytic con-
verter<Ref. to
EC(H6DO)-4,
Rear Catalytic
Converter.>
Front Catalytic Contact the SUB-
Converter<Ref. to ARU dealer.
EC(H6DO)-3,
NOTE:
Front Catalytic
Inspection by DTM
Converter.>
is required for fear
of deterioration of
some parts.
No