I just recently purchased an AVH 2550 NEX. I have the micro bypass hooked up that I had on an older model Pioneer deck. It does not work with the this new one. I’ve being seeing a lot of talk in other forums of “secret” menus that you can access by pressing certain buttons. Wondering if this applies to this deck as well and if so has anybody discovered it yet. I also updated the firmware to 8.6. 

Fixed it!

I am fighting the same issue on the same unit.

Can I ask how you did it, or point me in a direction please.

PAC TR1 Video Lockout Bypass Trigger Module

I have that installed - doesn't work on this model. The PAC provides ground in the triggered sequence.

This Pioneer is looking for power & then ground for the disable, which is ridiculous.

It never looks for a power. Only Ground. Radio needs to see double pulse Grd to bypass. I've done thousand of pioneer radio. Never had a problem. I always found a work around... I'd you can't do it. Take it to a professional.