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Home >> Alfa Romeo >> 2019 >> Giulia Base, AWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (2.9L Pcm 1 - DTCS P0351-00 To P06DB-00) >> DTC Troubleshooting >> P0420-00-Catalyst System Efficiency Below Threshold Bank 1 >> Possible Causes

Possible Causes

WARNING: This page is about a different variant/trim than selected.
Possible Causes
O2 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/1 RETURN CIRCUIT OPEN
O2 SENSOR 1/2 RETURN CIRCUIT OPEN
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER

Always perform the PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding. Refer to  PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE  .