Chevy and GMC Duramax Diesel Forum

Chevy and GMC Duramax Diesel Forum (
-   11-16 LML Duramax Powertrain (
-   -   2014 lml p0420 code (

Los1wing 11-19-2019 06:07 AM

1 Attachment(s)
I am on a road trip that started in south Georgia and I am on my way to Shiocton Wisconsin. I am towing an 18 ft flatbed trailer with a light load. 3000lbs including trailer. There are no mods on the truck. I am half way through my last tank of fuel.

I stopped at rest area and when I started the truck everything appeared fine. I saw the check engine lamp come on. I pulled off the highway to check fluids. Not finding anything, I drove on to a safer place to take a look and get my code reader that was packed away.

I came up with these codes:
P0420 three times.

I will attempt to clear the codes with my tool but I think a couple are permanent codes.

I'd like to know if I can continue to drive. Am I looking at a possible breakdown? Or is this just an emissions related issue?

Any information will be appreciated. Getting back on the road in 24 hours.

Sierraluva 11-19-2019 06:43 AM

Fill out your signature with info on your truck. That will help us fill in the blanks.

It looks like you’re CAT is sooted up or bad and your NOX sensors are faulty. Im afraid you may have succumb to the good ole emissions failure. This will most likely limit you’re speed if you continue.

Los1wing 11-19-2019 07:12 AM

Thank you. I reset the codes with the exception of the perm p0420 code. I will continue with the trip tomorrow. We will see how it goes. No power issues yet.

Ron Nielson 11-19-2019 08:19 AM

Has your truck gone thru the regen process on a regular basis?

This information is published for my 2008 LMM truck - yours may be different:
  1. Inspect for the following conditions, which may cause a diesel oxidation converter (DOC) to degrade:
    • Off Road Fuel or Red Dye Fuel
    • Low quality B-20 fuel
    • Fuel Containing high sulfur content
    • Engine oil or coolant consumption
    • Leaking fuel injectors
  1. Inspect the DOC for the following conditions:
    • Physical damage or alterations
    • Internal rattles caused by a damaged catalyst substrate
    • Exhaust leaks before or after the DOC.
    • If a condition is found, replace the DOC.
  1. If all exhaust system inspections are normal, replace the DOC.

Los1wing 11-19-2019 08:29 AM

It went through at least one regen since I left south GA. I only noticed because of the higher than normal idle at a traffic stop. After the codes I saw it go through a regen on my scan tool. It showed, on active 100%. When it was finished it said off passive 49% -52%

Los1wing 11-19-2019 09:49 AM

The truck does normally run it's own regen. The codes say cat inefficiency. And related codes were not sensors. So is my problem a clogged cat or clogged dpf? Does a clogged dpf cause the cat inefficiency problem? Thank you for your reply.

Los1wing 11-19-2019 10:27 AM

Finding someone competent is the problem. Especially since I am on the road. I can see many of the sensors related the cat and dog but I have no idea of what normal readings look like.

Los1wing 11-19-2019 03:27 PM

I am actually pretty scared to drive my Chevy with the emissions issues that I have had and now having. I don't have much choice at this point, I have to finish my trip back to south . Is Gereral Motors doing anything to address these emissions problems or just correcting them on newer models? I can't even bring my truck to a dealer for the code. After reading the post here, I'm not so sure I will get the help I need . Just a large bill to take care of a flawed emission system. I will update when I get home and the dealer looks at it, or on the side of the interstate.

Thank you all!

Los1wing 11-21-2019 06:11 AM

After clearing the codes the light went out but the p0420 remained. I drove 180 miles and when pulling off of the interstate, the check engine light came on with a service exhaust sys see owner manual. Then 99 miles until 65mph limit appeared . I read the codes and all were nox sensor loss of communication a and b and nox sensor voltage for a and b. The p0420 was gone. The truck is at the dealer here in Oshkosh. We will see what happens. The service writer stated that his last customer with these codes ended up with two nox sensors and the third visit fixed it with a dpf. I told him that I am 1200 miles from home and I can't afford 3 stops at the dealer. Gm protocol is one sensor at a time before the dpf is what he told me.

Los1wing 11-21-2019 12:13 PM

GM dealer, yes. I was told it needs the nox sensor 2. The problem is, if it fails, I will be on the highway for 1200 miles and stuck where if it fails. Has a box sensor ever fixed this kind of problem?

All times are GMT -7. The time now is 05:19 AM.

Powered by vBulletin® Copyright ©2000 - 2020, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.

For the best viewing experience please update your browser to Google Chrome