I have a 2005 645ci, last December I got a check engine light. "Increased Emissions". Took it to my BMW dealership and they informed me that it was a bad thermostat, for the $260 I had them just replace it. Car was returned and no check engine light present. I drove it till August and the same light popped back up. Took it back to BMW they informed me it was the same error. I told them to just replace the bad part it's under warranty. They informed me that there was a BMW Bulletin out about this issue coming up twice and refused to replace the thermostat, instead they wanted me to pay $2600 for a engine harness. If the light came back on after the engine harness was installed they would replace the thermostat for me. Pretty nice of them isn't it! I cleared the light, drove the care for 1500 miles at least and then the light popped back on. Cleared it, drove it again for 600+ miles popped up again, cleared it again took a road trip 2 hours away and back light popped up again and now after clearing it pops up after 5-30 miles. Got very frustrated with the whole process and complained to my BMW dealership. They said they would do the thermostat, in the process they replaced the temp sensor also. I got the car back on 11/1/2016 drove it home, went 10 min from my home and back, then back out 5 min and the light is back on. BMW has made me believe that the only fix is this engine harness. The car runs completely fine and normal. My gas millage has dropped from 17-19 mpg to about 16 mpg. I get the feeling since we live in Phoenix and it is Scottsdale BMW that people just throw money around at the dealership to get things fixed. I tend to do all DIY on my cars. This just does not seem right. Please advise!