Def Warning - Derate
5th Wheeling
Joined: Jan 2016
Posts: 46
Likes: 10
To avoid completely derailing the thread: My 2016 does this every once in awhile with DEF warnings. I refill the tank and the warning will reset itself after a couple of drive cycles.
Last edited by mini-x fan; Apr 5, 2026 at 12:06 PM.
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More Turbo
Joined: Jun 2023
Posts: 623
Likes: 264
Just an update. Although the “chicklet” symbol for the DEF issue went off yesterday the CEL was still on display until this morning when I started it. The display - I am happy to say (hesitantly) is back to normal.
More Turbo
Joined: Aug 2002
Posts: 539
Likes: 46
From: Lansing, MI
I thought I remembered it being 8yr/80,000. Google says this for a 2021 F350:
Key Emissions Warranty Details
Key Emissions Warranty Details
- Duration: 8 years/80,000 miles (whichever comes first) for major components.
- Major Components: Catalytic converter, electronic emissions control unit (PCM), and onboard emissions diagnostic devices (OBD-II).
- Other Emissions Parts: 2 years or 24,000 miles.
- Diesel Coverage: The 6.7L Power Stroke diesel engine, including many emissions-related items, is covered for 5 years or 100,000 miles.
Laughing Gas
Joined: Apr 2023
Posts: 931
Likes: 1,883
From: SE PA
I thought I remembered it being 8yr/80,000. Google says this for a 2021 F350:
Key Emissions Warranty Details
Key Emissions Warranty Details
- Duration: 8 years/80,000 miles (whichever comes first) for major components.
- Major Components: Catalytic converter, electronic emissions control unit (PCM), and onboard emissions diagnostic devices (OBD-II).
- Other Emissions Parts: 2 years or 24,000 miles.
- Diesel Coverage: The 6.7L Power Stroke diesel engine, including many emissions-related items, is covered for 5 years or 100,000 miles.
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More Turbo
Joined: Jun 2023
Posts: 623
Likes: 264
Best too make sure first.
For a 2021 Ford F-350 with the 6.7L Power Stroke, the factory emissions warranty is generally 5 years or 100,000 miles for diesel emissions components under Ford’s warranty guide and diesel warranty information. Ford also provides a diesel engine coverage period of 5 years or 100,000 miles for the engine and certain related components.[ford +1]
What is usually covered
The emissions warranty is meant to cover defects in emissions-control parts, not normal wear items or damage from misuse. For diesel F-350s, this typically includes major emissions hardware such as aftertreatment-related parts, depending on the exact configuration and certification.[ford]
Important exception
Some specific emissions components can have different coverage due to recalls or special warranty extensions. For example, Ford issued an extended warranty for certain diesel particulate filter issues on some 2021 vehicles, increasing DPF coverage to 10 years/185,000 miles or 10 years/110,000 miles depending on application.[nhtsa]
For a 2021 Ford F-350 with the 6.7L Power Stroke, the factory emissions warranty is generally 5 years or 100,000 miles for diesel emissions components under Ford’s warranty guide and diesel warranty information. Ford also provides a diesel engine coverage period of 5 years or 100,000 miles for the engine and certain related components.[ford +1]
What is usually covered
The emissions warranty is meant to cover defects in emissions-control parts, not normal wear items or damage from misuse. For diesel F-350s, this typically includes major emissions hardware such as aftertreatment-related parts, depending on the exact configuration and certification.[ford]
Important exception
Some specific emissions components can have different coverage due to recalls or special warranty extensions. For example, Ford issued an extended warranty for certain diesel particulate filter issues on some 2021 vehicles, increasing DPF coverage to 10 years/185,000 miles or 10 years/110,000 miles depending on application.[nhtsa]
Fleet Mechanic
Joined: Feb 2007
Posts: 1,320
Likes: 13
From: Mid Atlantic
I had this happen to me about a month ago. Made an appointment with the dealer for two weeks out! (The soonest they could get me in).
Then I figured I couldn’t be the only one and went online and found this video.
Although he uses his diagnostic tool to verify the temps basically you fill up the tank then run it in neutral at about 2300 rpm for about 25 minutes ( I’m not sure of the time) then drive it down the road and the warning will disappear. In my case it was probably caused by putting in def when I was below 1/2 full but not necessarily filling the tank which didn’t allow the sensor to reset.
Then I figured I couldn’t be the only one and went online and found this video.
Although he uses his diagnostic tool to verify the temps basically you fill up the tank then run it in neutral at about 2300 rpm for about 25 minutes ( I’m not sure of the time) then drive it down the road and the warning will disappear. In my case it was probably caused by putting in def when I was below 1/2 full but not necessarily filling the tank which didn’t allow the sensor to reset.
Cargo Master
Joined: Jan 2006
Posts: 3,013
Likes: 90
From: SE. MA
Here is a thread I started a few years back when I was having similar issues...
https://www.ford-trucks.com/forums/1737030-p2oee.html
https://www.ford-trucks.com/forums/1737030-p2oee.html
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More Turbo
Joined: Jun 2023
Posts: 623
Likes: 264
Started truck this morning here in St. Petersburg and the def warning ⚠️ came on again. I checked def gauge and it indicates 5500 miles to E. I decided to go to a local Ford dealer and on the way over the ‘chicklet’ symbol and warning turned off.
Frustrating to say the least.
Frustrating to say the least.
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Cargo Master
Joined: Jan 2006
Posts: 3,013
Likes: 90
From: SE. MA
Started truck this morning here in St. Petersburg and the def warning ⚠️ came on again. I checked def gauge and it indicates 5500 miles to E. I decided to go to a local Ford dealer and on the way over the ‘chicklet’ symbol and warning turned off.
Frustrating to say the least.
Frustrating to say the least.
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More Turbo
Joined: Jun 2023
Posts: 623
Likes: 264
In that other post I linked above there is a TSB that they performed on my truck, not just that emissions recal/reprogram. I do have the same year truck as you so I figured that could be it? I think my CEL went on and off aas well as the message appeard and disappeard but the code was still in the computer..
Darn EPA and these flaky emission regulations
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More Turbo
Joined: Jun 2023
Posts: 623
Likes: 264
Okay another update.
Put ~600 miles on the truck after leaving St Petersburg today. Truck played chicken with me giving me a warning that a derate upon restart would only allow me to travel 50 mph. When I restarted it all the warnings were gone and only CEL as left in display.
Interestingly my DEF Gauge reads full with the analog needle but the digital display says ‘65000’ miles until empty.
Think it might have a bad sensor.
Put ~600 miles on the truck after leaving St Petersburg today. Truck played chicken with me giving me a warning that a derate upon restart would only allow me to travel 50 mph. When I restarted it all the warnings were gone and only CEL as left in display.
Interestingly my DEF Gauge reads full with the analog needle but the digital display says ‘65000’ miles until empty.
Think it might have a bad sensor.
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