Will an OBD2 reader drain battery?
 

Answer: It sure as hell will! I experienced this unintentional unfortunate event over a two week period when I was gone. The reader and an old Android phone COMPLETELY emptied my battery of any life. I left it on a 2AMP charge overnight and she fired right up this AM.
I hadn't noticed anything unusual during a 15 mile jaunt this AM until I filled her up with fuel (diesel seems to work better than gasoline). The "distance to empty" now reads 100 miles too low. Is this to be expected? Will it correct itself? Do I need to take it to the Ford fix-it place?

I can live with the inaccuracy as the fuel gauge seems to be correct, but it bothers me. It seemed to have been accurate until I filled it up. Any advise? Ant similar experience from those not too embarrassed to admit they are as forgetful as I am?

2015 6.7 diesel Platinum.
Nearly Normal Mike

It shouldn't. Not sure about the CHEAP Chinese ones but the one I use to have never drained my battery the 6 months I used it. I would go weeks without driving the truck. They should power off after so many hours of inactivity.

https://www.scantool.net/obdlink-mx-...oth-scan-tool/

The M-to-E is in constant state of flux. It is calculated and recalculated with the way drive your truck and the load it carries

Do you reset the M-to-E after each fill up? If not, you should.

I admit my ignorance!
I did not know I could reset the DTE. I though it did it automatically. Would you please be so kind as to elorabate?

My car does it automatically and is amazing accurate given the different driving situations. I know how to reset it manually but there is no need as it does so on its own.

My OBD2 reader is admittedly a very cheap Chinese version. The readout display is an old phone I use as the display only, and it was also plugged in. I would have bet a bunch they would not have drained two batteries, but something did and I cannot find anything other explanation. No interior lights or anything.

On the DTE screen...You are actually resetting your Instant MPG. This helps reset the DTE calculations....DTE an go up or down.....sometimes when I refill my truck with the 65 gallon tank...it may read 850 MTE....and as I drive...it may recompute and go up to well over 999