I've seen around here a few threads about the M57 thermostat going soft. I wanted to know what the temperature threshold is to activate the CEL? I have a 2010 35d with 125k on it. It runs great, but I know for a fact my thermostat is definitely bad.

I live in northern VT and on the highway going 70mph engine temp never gets above 148F. My regens are still fine, but I thought that by now I would've seen a trouble code for my thermostat.