I'm having the same problems with another 2001 Montana. I've replaced the temp. sensor a couple weeks back and the engine light went off. After a week or so it came back on. The reading they had on the OBDII, was that the tempature sensor is reading below normal. JLSTMARY7 I would check to see where your gauge is at. My would stick around 1/4 but when the check engine light came on it wouldn't even come up.
Please post any progress as I will do the same.
Thanks,
Tony