Should be covered under the warranty. The cost through Chrysler is around $300 but the same part from MB is around $200. Once the relay control module has been replaced, which anyone can do in less than 10 minutes, the problem is solved.

If I remember correctly someone on one of the MB forums way back when posted close-up pictures of the circuit board in the relay control module to show where the problem was occurring. A search of the XF forums may turn up the link.