My 98 E300D has the diode/resistor EGR delete.

However, if I short start it (i.e. forget to wait for glow light) or have a hard time starting it (like after playing with the fuel system), mine throws P0400 and goes to limp mode.

I have taken to carrying a cheap OBDII reader with me at all times to clear the code and get it out of limp mode. Only had to use it once, while teaching my 15 yo son to drive, he hadn't quite gotten the rhythm down on the GP light and short started it, which threw it into limp mode. Luckily he did this in the garage so I didn't have to go far to get it, and it made me realize it should live in the car at all times.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech