My check engine light has went off and on?problems with dashboard gauges .

What is your question?

My speedometer is going 2 times faster than normal, my ac/heater temp. is also off.my thermostat was replaced but has not registered in the middle goes way off the gauge .what is the issues & the cost?The speedodometer ,& ac/heater gauges started not working correct forabout 2 weeks.The fan has gotten very loud.(inside)ac& heater.

What makes this problem better or worse?

Turn auto off.

How long has your 2005 Pontiac Bonneville had this problem?

Over a year . And newer issues recently past week