I was on the way home from a road trip to Idaho, about 500 miles out my DEF warning light came on and told me refill. Next station I put a jug in and expected the light to go away as usual. It did not. It kept popping on every 25-50 miles and then got to the point it warned me to keep speeds below 50mph. I started to get concerned that I may end up messing up my DPF system if it try to regen without using any DEF. I pulled into a station to get fuel that was across the street from a Ford dealership. I was going to pull over to the service department and ask them for advice but when I started the truck after filling up the light went off and everything was back to normal.

My question is should I be concerned about anything? Could I have a censor going bad? Anyone else have this experience before?

 

That's how they work. You can find many, many posts here on that very behavior. So, it's less like a fuel gauge and more like an unforgiving spouse...making sure you are aware that you almost let it run out and that it can ruin your day.

 

BTW, DEF (Diesel Exhaust Fluid - to reduce NOx emissions) and DPF (Diesel Particulate Filter - to reduce particulate {soot} emissions) have nothing to do with each other other than they are both forms of exhaust treatments. A DPF 'regen' would not be affected by what's going on with the DEF system. Cheers.

 

The DEF system certainly isn't perfect. To avoid strange problems like that I put in a 2.5 gallon jug just below the 1/2 mark.

BTW, DEF is not used for the regen process. Diesel fuel is used for the regen.

 

I just experienced the same issue. I had a return trip of 19 hours driving. The DEF dash gauge indicated just under half before embarking . Having never added DEF before and unsure about how many miles I could get out of the remaining DEF fluid in the tank, I added one jug of BlueDEF- ( 2.5 gals). Gauge showed just over half full when I started my trip towing a 16 enclosed car trainer with about 1000 pounds of cargo. About 75 miles from my destination the DEF warning showed up. Made it home without any problems. When I got up this morning I added one 2.5 jug of BlueDEF. Still got the dash warning when I started my truck. Then I added a second 2.5 gals. The warning message did not return when I started he truck and the DEF gauge showed full. I was thinking the maybe the DEF Tank must see a higher lever of the DEF fluid to cause a reset.

Side note about this trip: I was forced to use BioDiesel at one of the many fuel fill ups on the trip. I saw a 2 mile per gallon decrease on the mpg and 200 more (approx) RPM at the same speed, load and road conditions. The next stop I was able to find a truck stop and fill up with the normal #2 diesel. The RPM and MPG returned. In all I had to fill up 7 times, one with the BioDiesel. Road conditions varied due to elevations but other than that the other 6 fill ups gave consistent numbers.

 

I think it's just a screwy system.

 

Ok guys thanks for the info. Learn new stuff all the time. So to clarify the DPF and DEF are not connected or work together? I thought they did based on how many deleted trucks that no longer need to run DEF?

 

No, completely independent, designed to treat two different emissions issue, DPF to elminiate particulate, DEF to reduce NoX (smog).

the only relationship you would see is that during regen you burn more fuel with higher combustion temperatures, so you use more DEF. But the DEF usage is related to the fuel burn, not the particulate incineration.

 

Thanks for the info. Im relatively new to the diesel world so still learning. As a follow up, when someone "Deletes" their truck and runs a tune both the DPF and DEF systems are removed?

 

I all the time I have dealt with def, my practice was always to allow it to get to 200 miles to empty and then do a complete fill. Never have had a problem

If I am traveling out of my area then I take it along.

I never use the pumps at truck stops for def, Don't use it that much, about every 4-5K miles between fills.

I use the ford fill spout to avoid overfilling and spills.

 

General consensus seems to be that the algorithm for the gauge changed with the 2017+ trucks. Waiting until you get the warning isn't necessary. Some 2017+ owners have had issues with letting it go that long. I've had no issues by adding a 2.5 gallon jug when it gets just below 1/2. A theory on the DEF heater was posted within the past few months that said that going low on DEF may be detrimental to the DEF heater. I have no technical knowledge on that.

 

Yes, I am aware of the changes. I do understand keep the heater submerged but I just don't think that would be an issue if you fill it at about that point.

Wish we knew at that point how much is still in the tank, but that would be a moving target based upon usage.

 

When I add a 2.5 gallon jug, just below the 1/2 way point on the gauge, I've never had it overfill.

I don't understand why it's so hard to produce an accurate gauge for DEF.

 

Roughly $13 for 2.5 gallons of water and cat urine. What a scam.

 

My DEF gauge takes minutes to reflect any filling activity. My fuel gauge I can watch move in real time. For some reason, the DEF gauge takes forever to register any additions. Hopefully, all you experienced was that normal lag.

Any scam requires a rube. If you're paying $13/2.5 gal, then you're the rube. Should be about half of that, unless you own stock in BlueDEF and just want to see it do well.