Everything that I've found says that P218F has to do with DEF and not fuel. This is what the mechanic has communicated with me. It indicates that the quantity of DEF that's delivered is not what was commanded.
I've google the hell out of the code and the best thing I've found is this:
https://www.dtcdecode.com/RAM/P218F
The technician has ruled out everything except the pump, or at least that's what I'm being told.
There is a DEF filter that's supposed to be serviced every 100k. However, the pump is supposed to dispense 100ml of DEF in 6 minutes time. The mechanic has tested this flow rate (Ram has defined a test) three times that I know of and every time this flow rate has been perfect (in the exact middle of the expected range). The problem seems like it's intermittent and of very short duration. I've been getting the code for some time, and I've cleared it myself. I've seen it take over 100 miles to code again. I've never seen it re-code very quickly after clearing. Once it went for well over 100 miles. Whatever is broke is not staying broke.
Thank you for your response
Tom