Just received an AppRadio2 and ran into some issues. The headunit itself works fine; when I start the car, the radio comes on, the initial CAUTION message comes up, and after I click OK, the main screen displays. I can access the radio, settings, etc. When I connect the phone (and I've tried both my 4 and 4S) to access apps, I hear the chime that it's connected and charging, but the app icon on the screen never goes active - it stays greyed out.

Is there something else that I need to do? Does the cord need to be replaced?

Since you've tried two different phones I assume what I'm gonna suggest isn't the problem...

But, are they jailbroken with something like "No Accessory Splash" from Cydia installed?

I had this problem when I first got my radio and it didn't hit me until a few hours later while trying different things.

The 4 is jailbroken, running iOS 5; the 4S is not jailbroken and running iOS 6.1.

I'm not totally convinced it's the cable since the phones do chime and charge when connected, but I don't know what else it could be or where else to look.

Have you tried clicking on the pioneer app on your phone?

Sadly that sound exactly like a bad cable. Check the port itself. It may be dirty. That would be your best hope of getting the machine working again. 

Thanks. I went back and checked all of my wirining, checked the connections for any broken leads and such, then I took a can of compressed air and did thorough cleaning on all male and female connectors. I guess something got dislodged or was in the wrong place because now it works like a champ!!

Now to wire the microbypass and dremel a pass through for the cable, then I can finally put my dash back together!

Glad to hear we could help. Enjoy your radio.