DEF system fault pump
A). That is a statement, not a question.
B). Get it fixed.
Actually, not even a complete statement.
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I didnât realize the DEF required a system fault pump. I always thought gravity was the default pump 
I guess this is shorthand for ( Code is for DEF system fault â Usually means the DEF pump is bad ) . Of course we will probably never know . What are people like this going to say when they have to go to the Doctor ?
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Truck will probably still run ok, but the DEF problem may prevent the truck from passing any required state/county emissions testing. First step, make sure the DEF tank fluid level is good, and the wiring harness in that area remains connected. . Beyond that, somethingâs likely broken. I expect most any shop w/diesel experience would be able to fix this for you.
Check with your dealer. The DEF system may be part of the emissions system warranty.
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this is inaccurate. Engine manufacturers presented the DEF/DPF/SCR systems to the government as a way to curtail emissions in diesel engines. As such, the Government said- âok, cool. Now make sure it works all the time.â So unless an illegal computer bypass has been done, a emissions system fault will cause the ECM to derate the engine until repairs are made. Damage to the engine is not likely, but it gets real old, real fast only being able to do 4 mphâŚ
the rest of this is good. 
Yes, check this. The government also insisted that these systems have a much longer warranty period than the rest of the vehicle. Iâve seen some as much as 8 years, 100,000 miles.
The warranty pamphlet that came with the vehicle explains this clearly. If you donât have it, you can find one online. A quick search turned up this example for 2019:
EMISSIONS PERFORMANCE WARRANTY COVERAGE
Under Emissions Performance Warranty Coverage, Ford Motor Company
will repair, replace, or adjust - with no charge for labor, diagnosis, or parts -
any emissions control device or system, if you meet all of the following
conditions:
⢠You have maintained and operated your vehicle according to the
instructions on proper care in the Ownerâs Manual and this booklet.
⢠Your vehicle fails to conform, during the warranty coverage period, to
the applicable national EPA standards, as determined by an EPA
approved inspection and maintenance program.
⢠You are subject to a penalty or sanction under local, state, or federal law
because your vehicle has failed to conform to the emissions standards.
(A penalty or sanction can include being denied the right to use your
vehicle.)
⢠Your vehicle has not been tampered with, misused, or abused.
The warranty coverage period for:
⢠Passenger cars and light duty trucks (applies to vehicles up to 8,500
pounds GVWR) is as follows:
â 8 years or 80,000 miles (whichever occurs first) for catalytic
converter, electronic emissions control unit, and onboard emissions
diagnostic devices.
â 2 years or 24,000 miles (whichever occurs first) for all other
covered parts .
⢠Heavy duty vehicles (applies to trucks over 8,500 pounds GVWR up to
19,500 pounds GVWR)
â 5 years or 50,000 miles (whichever occurs first) for all covered
parts.
See WHAT IS COVERED? below for list of covered parts.
Note that the warranty period begins on the Warranty Start Date as
specified on page 2 of this booklet.
19
WHAT IS COVERED?
For your vehicle if these parts contain an emissions-related defect, they
are covered by both the Emissions Defect Warranty and the Emissions
Performance Warranty.
⢠Air Flow Sensor
⢠Air/Fuel Feedback Control
System and Sensors
⢠Air Induction System
⢠Catalytic Converters (including
Selective Catalytic Reduction
and Diesel Oxidation Catalysts)
⢠Cold Start Enrichment System
(diesel only)
⢠Controls for Deceleration
(diesel only)
⢠Diesel Exhaust Fluid System
⢠Diesel Particulate Filter
⢠Electronic Ignition System
(diesel only)
⢠Electronic Engine Control
Sensors and Switches
⢠Powertrain Control Module
(PCM)/Engine Control Module
(ECM)*
⢠Evaporative Emission Control
System
⢠Exhaust Gas Recirculation
(EGR) System
⢠Exhaust Manifold
⢠Exhaust Pipe (Manifold to
Catalyst)
⢠Fuel Filler Tube and Seal
(non-diesel only)
⢠Fuel Injection System
⢠Fuel Injector Supply Manifold
⢠Fuel Tank (non-diesel only)
⢠Fuel Tank Pressure Control
Valve
⢠Ignition Coil and/or Control
Module
⢠Intake Manifold
⢠Intercooler Assembly -
Engine Charger
⢠Malfunction Indicator Lamp
(MIL)/On-Board Diagnostic
(OBD) System
⢠PCV system and Oil Filler Cap
⢠Secondary Air Injection System
⢠Spark Control Components
⢠Spark Plugs and Ignition Wires
⢠Thermostat
⢠Throttle Body Assembly (MFI)
⢠Transmission Control Module
(TCM) and Solenoids
⢠Turbocharger Assembly
⢠Vacuum Distribution System
- Includes hardware and emissions related software changes only
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Interesting, didnât realize such a speed restriction could happen for no other reason than govât fiat, thanks for the update. Iâm sort of surprised the federal govât would purposely limit an ownerâs vehicle to 4 mph simply b/c the DEF tank was empty. Seems like there could be personal safety implications, putting the govât at risk of a big $$$ legal settlement, if for example the owner was being chased by a gang of hoodlums, and got attacked and beaten, simply b/c their carâs DEF tank was empty. Life in America I guess.
Well, this is kind of the victimâs mentality. Itâs not my fault because I didnât do proper maintenance on my vehicle, itâs because someone else didnât allow that lax approach toward maintenance to be overlooked.
What about other situations like triggering the limp mode? Wouldnât car makers be liable for engaging that in the instance a wild group of unicorns just happened to be chasing your car down the street intent on goring you to death?
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This seems to indicate the DEF system is only covered for 2 years/24K miles if the vehicle is 8500 pounds or less, or 5 years/50K miles if itâs above 8500 pounds GVWR. Either way, a 2016 is past the warranty period.
If youâre driving at the time it runs out of DEF, you will be able to continue driving.
Itâs when you restart the vehicle that it will limit the speed.
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Good info, thanks @It_s-Me . Still a little confusing why DEF would be treated diffeently than say a leak in the evap system. Both affect emissions, but I donât think vehicle speed is restricted when thereâs a leak detected in the evap system. Maybe whether to impose a software limit on speed or not, itâs a matter of how detrimental to the environment it is? Sort of makes me uneasy thinking of a room full of political appointees deciding when to limit my carâs speed tho.
Because keeping DEF in the tank is normal daily maintenance, not a repair.
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not always.
I know Chevyâs will give you several hundred miles of warning, then just start de-rating vehicle speed, without an engine shut off/restart. Not positive on other makes.
From the 2016 Ford F-350 Diesel Engine Supplement
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50 while driving is not key off circumstances.
âlimited to idle speed only once stoppedâ
I take that to mean when vehicle comes to a stop, not when shut off. I donât have personal experience with the Fordâs, so I cannot say for certain. Either way, they are pretty serious about making sure your diesel has DEF in it.
Not disputing the facts, but seems an out of proportion & unsafe policy . IMO it would be better for carâs dashboard to give a warning when out of DEF, with 4 weeks advance notice before any vehicle operation restriction. Even then, worse case should be a limit to 35 mph. Otherwise the owner may get stuck in the wilderness or bad area of town w/no way to extricate themselves.
Is 500 miles enough warning ?
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Yeah, 500 miles seems ok, but imo even if warning ignored and DEF runs completely out, 35 mph limit. Owner could still get out of trouble and I expect 99% of owners would soon refill DEF rather than having a 35 mph limit. Isnât perfect, but perfection very expensive and unsafe.
This topic would make for interesting Car Talk column.