2015 Ford F750 DEF Issues

Hi all,

I keep getting the SPN 5934 FMI=5 code which is related to the aftertreatment dosing valve. This occurs every morning when I start up the truck. After driving for about 30 minutes, I turn off the engine and I can reset the computer and it's good for the entire day of driving, until the next morning.

I'm in Los Angeles, CA.
DEF Header in the tank was replaced a year ago. The old one went bad after 7 years. The level sensor (sonic vs float) was bad. DEF level were erratic even though the level is usually 1/2 tank or more.
Doser valve assembly changed out.
Doser valve resistance checked, 12.3ohms
Doser valve opening cleaned
DEF Pump filter replaced.

The only thing left I can think of is maybe the DEF pump? BTW, DEF fluid level in the tank is decreasing normally and I have to refill it at the normal intervals. The DEF is not leaking anywhere that I can see. No white powder buildups.

Help! Thanks.

 

Found the problem.

Bad def in the tank. While I've been using Walmart supertech def for 7 years without issues, this last 3 jugs caused the cel codes. After switching to peak blue def from the almost empty tank, code is not coming up.

I don't think the problem is directly with the def itself but how it's packaged. The Walmart cheap flimsy seal vs a more tight seal on bluefdef prevents evaporation and/or contamination.

What put the final nail in the coffin was when I was at a Walmart gas station and noticed some Walmart def jugs were sitting in direct sunlight in one of their displays.

Bluefdef can be bought for 2 cents cheaper than Walmart at home Depot.