Attention: TDR Forum Junkies 
I have been having excessive DEF usage, and dealer reflashed the ECM, and it is better.
After the reflash, the gauge seems to hang on "Full" longer.
The service tech got ahold of RAM, and this is their answer:
"There is NO sender float in the DEF tank. Because DEF freezes, they could not use a conventional float system, because the ice would damage it. "
I can see that. As the solid block of DEF melts, it would be like a giant ice cube, with the float and arm frozen in it, and as it sloshed around, it would be broken.
"So, the sender is a RF type that uses a signal to determine the DEF level, like radar. However, the RF sensor is not accurate when the tank is near full, so until the level drops to about 60% full, the computer figures out how much DEF you should have used, and that is what shows up on the gauge."
So, if you pull a load, and are using DEF faster than normal, the computer inputs normal DEF usage to the gauge, and it does not drop much, even though you are using more DEF. Then, when it gets to about 60%, the actual level is used by the RF sensor, so the gauge drops rapidly.
It came up because while we were checking the DEF usage, I pulled hard, but my gauge was still on the full line, although you could tell it had dropped a little. The tech put 2 gallons in the tank, so we were trying to figure out what was wrong with the gauge. This is the explanation from RAM.
Makes sense to me. I was just at the point were the RF sensor would take over, and my gauge would have dropped fast pretty soon.
After the reflash, the gauge seems to hang on "Full" longer.
The service tech got ahold of RAM, and this is their answer:
"There is NO sender float in the DEF tank. Because DEF freezes, they could not use a conventional float system, because the ice would damage it. "
I can see that. As the solid block of DEF melts, it would be like a giant ice cube, with the float and arm frozen in it, and as it sloshed around, it would be broken.
"So, the sender is a RF type that uses a signal to determine the DEF level, like radar. However, the RF sensor is not accurate when the tank is near full, so until the level drops to about 60% full, the computer figures out how much DEF you should have used, and that is what shows up on the gauge."
So, if you pull a load, and are using DEF faster than normal, the computer inputs normal DEF usage to the gauge, and it does not drop much, even though you are using more DEF. Then, when it gets to about 60%, the actual level is used by the RF sensor, so the gauge drops rapidly.
It came up because while we were checking the DEF usage, I pulled hard, but my gauge was still on the full line, although you could tell it had dropped a little. The tech put 2 gallons in the tank, so we were trying to figure out what was wrong with the gauge. This is the explanation from RAM.
Makes sense to me. I was just at the point were the RF sensor would take over, and my gauge would have dropped fast pretty soon.
