[udm328i]

Is it definitely the thermostat? Is there a way to check ect sensor, would that throw a different code?
Engine temp was reading 188° F
Turned on fan and was getting heat in the car.

[mike3000fl]

When the thermostat fails on our cars, it usually gets stuck in the open position, not the closed position. This is significant because if it stuck in the closed position, no coolant would flow through the radiator and the car would overheat. Since it gets stuck open instead, the coolant continually flows thru the radiator and the cars coolant temp is actually lower than it should be at times. That's probably what that error is.

On a normally functioning system, the thermostat is closed so that the car can warm up, then once it has warmed up and gets hot enough, the thermostat opens and allows coolant to pass thru the radiator, which then cools the car down.

Originally Posted by udm328i

Turned on fan and was getting heat in the car.

The reason you still get heat is because the water pump is still working, so it is still pumping coolant thru the system and to the heater core also.

Oh, you may notice that your engine fan will start running nonstop loud and fast like a jet engine, this is usually a sign of a failed thermostat too.

If you live somewhere warm and hot, like FL, you could run with a failed thermostat for awhile. If you like somewhere cold as shit, and your thermostat is stuck open, your car may never reach optimal running temps. You fuel economy may take a hit. 188F works out to about 87C, which seems low to me, my car runs high 90s C and just over 100C at times. (BMW variable speed electric water pump allows the ECU to vary temps as needed for fuel economy or performance, normal cars have a belt driven water pump which moves faster as RPMs increase).

If you are going to fix the thermostat, fix the water pump too, fun times.

[Efthreeoh]

All that code means is the electrical heating element in the t-stat is not working and is affecting the cold start emissions of the engine (which is why the SES light is illuminated). The t-stat is working fine regulating the coolant temperature (it works just like a normal thermostat); it's just the heating element is bad. This is a common failure with the t-stat.

[udm328i]

Do I need to replace t-stat asap? Can you explain a little bit about the cold start emissions

*is the heating element reducing emissions by getting the engine up to operating temps in a shorter amount of time?

[Efthreeoh]

When my car got the t-stat c ode it was when the weather turned cold in January 2010. I let it go through the next summer and the SES light remained off until November 2010 when it got cold again. I let it go a bit longer and changed the t-stat out in February 2011. Overall I drove about 34,000 miles between the first instance of the code appearing and when I changed the t-stat out. The Federal emissions requirements require reduction of cold start emissions (i.e. when the "choke" is used to enrich the fuel mixture to aid in engine starting in cold weather conditions). The N52 engine reduces cold start emissions by using an electric coolant pump that allows the coolant to heat up faster and locating the catalytic converters in the exhaust manifolds to allow for quicker lightoff of the catalysts.

[udm328i]

OK thanks for info