1) Does this replace a chip or add to it?
Re-programs your current ECU
2) Electronically undetectable? -- Diagnostics won't see any revision history?
No revision since the base ECU software remains unchanged
3) "Tucks away from site"? -- What are the chances and consequences of it actually being seen?
IMO unless you're looking for it you won't see it. Your ECU is like any other computer, it has a BIOS, an OS and programs. At the risk of oversimplifying the BIOS and OS are unchanged, those are the revision histrories you see when you pull the ECU firmware #'s.
EDIT: I do have a customer that worked with the DMV in California. He claims that the newer machines (smog) can detect changes to software but that has not been proven. IOW I have never heard of anyone failing over the detection of software.
Last edited by vmwerks; 01-24-2006 at 10:32 AM.