Good Chance this is caused by a faulty O2 Sensor. I had the engine light stuck on in my 2002 Montana and replaced rear O2 sensor and it turned it off.
If all of the dashboard lights do not work at the same time on a Pontiac Montana, check the instrument panel relay. The relay is located on the firewall in the engine compartment.
pontiac g6 check engine light car with wrench
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
if its not under the dash check under the hood
Check out this site. http://www.fueleconomy.gov/feg/findacar.htm
Check front end for play.
You should check the thermostat and the fuse for the heater.
Check out this site. http://www.fueleconomy.gov/feg/findacar.htm
You could be having a problem with your spark plugs and your dashboard is alerting you. You should have a mechanic check it out.
yes i advise changing it
At your local Pontiac dealer or an auto salvage yard. Check Ebay and Craigslist.org.
check and see if your thermostat is stuck open(top of engine block). depending where you live, water could be slushy or frozen in your engine.