Originally Posted by ForTheD
So I had the SES light pop on a few weeks ago, check it, P0128 (Coolant Thermostat Malfunction), erase it.
It comes back about 6 days later.
The car is acting just as normal including the heater and the engine response.
I have owned this car for the last 6k miles, and the temp always takes about 10 to 15 minutes to get to 220 or so, and there seems to be no change there.
Searching around I did not find a concrete fix for it, other then a the one person I saw replace the thermostat. This seems a bit extreme so I wanted to see what you all thought.
Is there a separate sensor somewhere?
p.s. I'm not taking it to the dealership. out of warranty and I like doing this stuff my self (with the help of the forum of course.
It's most likely the heating element in the thermostat not functioning properly. The thermostat is electronically controlled and has a heating element in it (not really sure of the function it performs). My car has the same problem, which cropped up last winter. I kept clearing the code until the Spring came hoping it would correct itself. All summer the code did not reappear, but in November, when it got cold again, the code is back. Changing out the T-stat is the only fix.
The good news is the T-stat has been redesigned, so hopefully BMW has addressed the problem. Second, the T-stat is designed to fail "open" so if it stops functioning it will not stay close and overheat the engine.