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Home >> Chrysler >> 2011 >> 300 C, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1572 (6.7L Diesel - DTCS P0402 To P0653 - 2500 Hd) >> DTC Troubleshooting >> P0421-Catalyst 1 Efficiency Below Threshold Bank 1 >> Possible Causes

Possible Causes

WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
POSSIBLE CAUSES
AFTERTREATMENT DIESEL OXIDATION CATALYST (DOC) HAS BEEN REMOVED FROM THE DIESEL PARTICULATE FILTER (DPF) CANISTER
AFTERTREATMENT DIESEL OXIDATION CATALYST (INSIDE THE DIESEL PARTICULATE FILTER (DPF) CANISTER) IS DAMAGED OR NOT FUNCTIONING PROPERLY
EXHAUST GAS TEMPERATURE SENSORS 1, 2, OR 3 ARE DAMAGED/FAILED
IMPROPER FUELING
WIRE HARNESS

Always Perform The PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE Before Proceeding. Refer To  PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE  .