2017 - 2022 Super Duty - 2020 F350 6.7 speed limited to 50mph - Due to a DEF problem. I ran the truck out of DEF and it got limited, truck sat outside in the cold for a couple days, filled it up, DEF gauge reads full but it still gives me the derate. Tried pcm relearn with forscan and no luck. Drove it 60 miles and.. 2017 - 2022 Super Duty - Help! May Be Stranded DEF Fault - Traveling 70E out of Higginsville, MO (east of St Louis) towing my 38 ft 5th wheel. Got a DEF warning DEF Fault speed will be limited to 50 mph in 50 miles. Found a Ford dealer, drove up & they are out of business. Great! On the forum people complain about.
DEF system fault is a common issue for more or less all types of vehicles containing this system. But truck owners have been reported to face it more frequently. The Ford F-series, 6.7 L PowerStroke trucks, fall under that category.. For Ford trucks, it shows you have about 5 miles to cover before your speed gets limited to 50 MPH... 2017 - 2022 Super Duty - 50 MPH DEF Fault - Good day Gents Hello I am new to the site and am looking for Help/advice I have a 2019 F-350 with a 6.7 Diesel. I had a DEF fault code come on yesterday and limped home. I connected my Jaltest diagnostic and run a fuel real time scan it showed no codes.. If you are getting a 50 mph speed limitation.