AutoCodes – Chevrolet – P0421 Chevrolet

P0421 Chevrolet Code - Catalyst 1 Low Efficiency

Quick Answer

The main function of the Close Coupled Diesel Oxidation Catalyst (CCDOC) is to control emissions of non-methane hydrocarbons and Carbon Monoxide (CO). Common causes include Faulty Oxidation Catalytic Converter, Faulty Diesel Particulate Filterâ€‰(DPF). Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0421 Chevrolet indicates Catalyst 1 Low Efficiency.
Common causes: Common causes include Faulty Oxidation Catalytic Converter, Faulty Diesel Particulate Filterâ€‰(DPF).
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

Save to My Repairs Step-by-Step Diagnostic Guide My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 661

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Sep 23, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Cost to Diagnose
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code P0421 Chevrolet Description

The main function of the Close Coupled Diesel Oxidation Catalyst (CCDOC) is to control emissions of non-methane hydrocarbons and Carbon Monoxide (CO). Its secondary function is to assist with the Diesel Particulate Filter (DPF) regeneration, by obtaining and sustaining the temperature necessary for regeneration. In order to generate the high exhaust temperatures needed for regeneration, the aftertreatment system increases exhaust temperatures by injecting diesel fuel into the exhaust system via post-injection. The injected fuel is converted into heat by the DOC to incinerate soot accumulated in the DPF. The Engine Control Module (ECM) monitors the exhaust gas temperature sensor 1 and 2 to determine if catalyst downstream temperatures are achieved during a DPF regeneration.

OBDII Code P0421 Chevrolet - Catalyst 1 Low Efficiency - AutoCodes.com — P0421 Chevrolet Code - Catalyst 1 Low Efficiency

What does this mean?

What are the Possible Causes of the DTC P0421 Chevrolet?

Faulty Oxidation Catalytic Converter
Faulty Diesel Particulate Filterâ€‰(DPF)

How to Fix the DTC P0421 Chevrolet?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0421 Chevrolet code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0421 Chevrolet code?

Need more information on how to fix the P0421 Chevrolet code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0421 Chevrolet code diagnosed by a professional: Find a repair shop in your area

Information for Specific Chevrolet Models

P0421 2014 Chevrolet Silverado — Catalyst 1 Low Efficiency
P0421 2015 Chevrolet Silverado — Catalyst 1 Low Efficiency
P0421 2016 Chevrolet Silverado — Catalyst 1 Low Efficiency
P0421 2017 Chevrolet Silverado — Catalyst 1 Low Efficiency
P0421 2018 Chevrolet Silverado — Catalyst 1 Low Efficiency

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.