Hi there folks small question just wondering what the difference is on the edc16u1 edc16u31 and edc16u34 are because I've done a few Jettas over the past couple weeks and when reading and writing a file on MPPS I have selected all 3 of the above ecus before ID'ing and it seems to make no difference either way why is this?

Are the 3 above ecus the same? And is there a specific year that has a specific ecu?

They are not the same, U1 has 1mb flash, U3x has 2mb flash and other MPC's. U1 is early 2004 , the rest are newer ecu's