Okay, so I started getting the "Fuel Tank Cap Loose or Missing" message after I filled up with gas about two months ago. Let it go for a while and finally decided I would order a new cap to see if that was really the problem. Seemed to fix the problem for about a month, but now the message is back again.

Any suggestions on how to diagnose where my evap emissions control system leak is coming from? I've seen a few comments around the DMTL valve, but is there any way to see if that's really the culprit? I don't really want to go throwing money at this thing without a plan, but don't have a fancy smoke machine or anything at my disposal.

 

And FYI, I have P0442-00 (E8) Evaporative Emission System Leak Detected (Small Leak) showing on the IID Tool.

 

The good news is that after about a week of driving, my Missing Fuel Cap message quit displaying.

In brief, I gassed up but forgot to screw the gas cap back on - first time in how many years so that was something new - always something new in a 3 no matter how long you have owned it.

The message did not display until my second engine startup after fueling up and forgetting to screw it back on.

I then stopped the 3, screwed the cap back on and drove away. It took about a week of engine starts for the message to self disappear.