Originally Posted by trader4 (Post 1048337)

These engines have a rather bizarre thermostat system, one that I have never seen in other cars. What they do is this. They operate the engine
at as high a temp as possible, most likely for emissions and/or other
reasons. But apparently under extreme load conditions, there isn't
enough margin and parts of the engine could overheat. So, what they
did was come up with a fancy thermostat that is like a regular mechanical
thermostat, except they added a heater. When the computer detects
that one of those extreme load conditions is occurring, it energizes the
heater in the thermostat, fooling the thermostat into opening fully
earlier than it otherwise would.

That code is apparently telling you that something is wrong with that
thermostat heating circuit, most likely the thermostat itself. If you
have access to INPA type software, I'd read out the full codes and
there should be more info there as to the fault. If that's what it is,
it's not a critical repair, provided you're not driving under extreme
conditions, the engine heavily loaded, etc.