Who did the testing? Was it the dealer? Take the VX back then.
You may want to go to an Autozone where they can call up the code that is throwing the check engine light. I think the cost is $10 and you can know for yourself what the problem is.
Maybe try this before going to the dealer.
Disconnect the battery for 10 minutes and reconnect. If the check engine light comes back on then by all means go to the dealer.
Good luck!