Yea, this sounds like the CPS. $55 shipped from Autohaus.
The Chrysler dealer will probably screw around for hours and try replacing $1500 modules until they happen upon the CPS.
You'd be better off having it towed to a small independent shop that works on Mercedes. THOSE guys have seen this before, your Chrysler dealer? Well, you MIGHT get lucky IF they have a mechanic who is familiar with the car... but not likely.
YOu are not driving a Chrysler.
I'd get that car towed the HELL away from that Dealer before they telll you
"The PTCM and CPS are both bad, parts ordered, they will be here in a week - $450 diagnostic charge plus $2400 for parts, call it $2500 and it's a deal". 
Then go to Autohaus in Arizona and order the CPS. It'll take 5 minutes to change it. THEN - Take the RCM out and either resolder it yourself or take it to a radio shop and let them re-solder the whole damn board, that will cost you probably $5 to $50.
And yer done.
(But I still agree with Woody, it's the damn CPS - anyway, the RCM will fail sooner or later anyway. MIght as well resolder it now!)