2003 VLX Engine Temp Gauge

We have recently been having a problem with the engine temp gauge on our 2003 Malibu VLX. Up until about a week ago the gauge had always read correctly, right at 160. But last week the gauge started to settle in at about 100-120 degrees when warm, and it never got close to 160. Have any of you guys seen this before? Is the gauge going bad? Or is it something else?

I hate not knowing what actual engine temp is!

Thanks in advance for your help.