P0420

DTC P0420 - CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD

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 and INSPECTION MODE. Refer to How To Clear Diagnostic Trouble Codes. Clearing Diagnostic Trouble Codes




WIRING DIAGRAM

10AG1: CHECK ANY OTHER DTC ON DISPLAY.

CHECK: Does the Subaru Select Monitor or OBD-II general scan tool indicate DTC P0130, P0133, P0136, P0139, P0141, P0301, P0302, P0303, P0304, P1130, P1131, P1132, P1133 and P1151?

YES: Inspect the relevant DTC using "10. Diagnostics Chart with Trouble Code".

NOTE: In this case, it is not necessary to inspect DTC P0420.

NO: Go to step 10AG2.

10AG2: 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 catalytic converter.

CHECK: Is there a fault in exhaust system?

YES: Repair or replace exhaust system.

NO: Go to step 10AG3.

10AG3: CHECK REAR CATALYTIC CONVERTER.




Separate rear catalytic converter from rear exhaust pipe.

CHECK: Is there damage at rear face of rear catalyst?

YES: Replace front catalytic converter and rear catalytic converter

NO: Go to step 10AG4.

10AF4: CHECK FRONT CATALYTIC CONVERTER.




Remove front catalytic converter.

CHECK: Is there damage at rear face or front face of front catalyst?

YES: Replace front catalytic converter.

NO: Contact Subaru Of America service.

NOTE: Inspection by Subaru Subaru of America's DTM is required, because probable cause is deterioration of multiple parts