Does erasing OBD2 codes using a code reader really erase all codes or just mark them as cleared.

Question

I mean could Ford or whoever not read the older codes in some log kept on the ECU with their "Ford" OEM reader?  From reading other posts I am just curious.  Any techs actually know?

Thanks!!

Answer 1

Some readers will be able to tell you that there was a old code in the system when though it was erased. You can leave the battery disconnected overnight and it should clear all the codes.