So far all we have seen is the EPA side of the conversation. VW's wording of the event may differ.
Understood, but the EPA (or CARB) saying VW admitted to breaking the rules against defeat devices when they didn't would likely put those entities in some real danger of paying some large monetary damages to VW for tarnishing the brand.
My whole point is that if VW is going to take the damage to the brand willingly by admitting the issue exists, they've very likely got a fix ready to go to kill the story. Heck, EPA could even have demanded the recall without an admission of guilt from VW I would imagine.
The fact that this was dropped on media garbage day (Friday) might speak a little to the issue as well. I'm sure if the EPA wanted to make a real issue of this it would have dropped this, or last, Monday where the story could be on the nightly news for a week.
They've got to have a fix, it's the only thing that makes sense. EPA says they want the credit for fixing the environment, If VW admits there's something wrong the EPA will release it on Friday. VW announces the fix Monday, recalls the cars on the roads, fixes the cars at the port and moves on. EPA gets good press, VW takes a sufficient (but smaller than it could have been) hit on the brand, it's all over by next week.
I'm only taking public perceptions, media, and politics into account, no clue if the technical fix is even possibly simple.
Edit: Speaking of politics. Did Chattanooga unionize? That could come into account with an executive agency as well. (I'm not really trying to make it political, just looking for answers in the puzzle pieces.)