Ok, the code kept coming back each time I cleared it. Pretty much about 40 miles to the mile after clearing the code it would pop the check engine light. I borrowed a friends ICarSoft MB II code reader for Mercedes and it came up with the code.......P20BD, which is for "Redundant heater "B" (DEF) circuit low or no voltage.

Sooooo. it appears that the DEF tank heater took a dump. Before I throw $400+ on a new heater unit, does anybody have any good troubleshooting tips or even better, a schematic of the heater circuit that I could use to narrow it down?

Many thanks

__________________
2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)