The gage fault indicator on my '08 Trailblazer came on along with the temp gage not working. This is the second time in less than 2 years. Last time I replaced the thermostat and all was fine until two weeks ago. When it happened then it was not giving any heat. Eventually the gage came back up, the fault indicator went off and all was fine, until today. Same thing occurred but it WAS producing heat, just enough to provide some comfort. The last time it happened, (2 years) it was not producing any heat. I replaced the thermostat, the old one was stuck closed, and all has been fine until now. Could it be that this time the thermostat is stuck partially open, (or partially closed) or should I be looking at another cause? My code reader gives a p018.