After the dealer replaced my ecm (and a few more electrical items)on my '16 Ultra Limited, I gained 20k miles on my odometer. How can changing a ecm changed the odometer itself, could they of used a previously installed ecm from another bike?

Thanks in advance for any comments

 

I believe the odometer gets the mileage from the ECM. At least when my wife replaced the speedometer on her 2009 Crossbones the new speedometer picked up the mileage as it was on the old one. Maybe the dealer had to do something to make it interface, I know it came with a cable.

 

They usually take it for a test drive after work is done on the bike. Maybe they just really wanted to be sure it was fixed

 

very true on some older ones using speedo storage and newer the ecm. however, there should be no additional mileage and if so, make the dealer correct it. if the ecm was new, the dude that flashed it probably was off!!! the mileage is stored in a rom and not ram so once burned in, can not change. if they refuse, ask for the dealer's factory rep. it may be only 20k but it makes a diff for value.
on some of the old car systems, there was a special software that could access the speedo but i do not think hd allows that.