I checked the IAT sensor and found it to be open (sensor wire broken). I cleared the code, disconnected the connector from the IAT and got the same 13 blinks on the LED. It looks like that is the problem. Part is on order. I have a little trouble with the MBZ CD-ROM Service Manual. I am an aircraft mechanic and not a MBZ mechanic. It takes me a little longer to figure this out. Thanks for all the help.