Just had my Check Engine light come on, the code was P0116, "Engine coolant temperature circuit range/performance problem". Lately I have not been getting much heat, Temp. gage barely at 5:00 on 30 degree day, probably a thermostat stuck open. My question is, will a stuck open thermostat set off this code, or is the sensor going bad and should be replaced as well. Also, I can't seem to find anyone who carriers the sensors online, is this a Volvo only item?

Thanks for your replies, Ray.

I had the excact same prob. I even posted the problem some time ago... the dealer replaced part. But its a DIY job.
It's about a ~$200 US service if the dealer replaces the Stat and the Sensor.
D~

I just had the same thing, changed Thermostat only and light did not come back on.
However I was getting a lot of smoke at startup when the stat was failing, it is down quite a bit now, barely noticeable.

See this thread:
http://www.brickboard.com/AWD/index.htm?id=595029

Did yours do this?

No, I did not have any smoke at start up. I just finished changing the T-Stat and clearing the code. Fairly easy job, although the 40mm torx was on really tight. I thought I was going to break my socket, but it came out. We'll wait and see if the code ever comes back. BTW, it's nice to have heat back. T-stat was not stuck open, but probably was weak.

Its a common problem. I just changed mine and I didn't change the ECT. Try changing the t-stat and o-ring and get the light reset first. That should fix it. If you still get the light, then go for the ECT. I went ahead and completely changed the coolant after that. (optional) I wimped out and got the Volvo coolant.