Troubleshoot a Code Reading

[Palf70Step]

2002 Silverado
4.3 V6, automatic, about 140,000 miles

Driving to work this morning, just as I pulled in the parking lot My service engine light came on. Drove home, light still on, ran code reader on it and came up with

P0128 - Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)

Checked coolant level, is right where it should be in tank and overflow bottle.

It's been cold (for Mississippi) last couple mornings and I noticed that my 15-20 min drive to work (35-40 MPH) truck only register say 160-180 on the temp gauge. On the way home around in the afternoon it reads up around the normal 200.


Quick net look says something about not reaching operating temp quick enough and normally means thermostat, which the way it reacts, doesn't seem that way.

Still runs great, no issues. on the truck. Heat works & everything that would lead to say a thermostat problem isn't registering with me.

You guys think thermostat, or is there something else that may effect it?

I was thinking about resetting the code to see if it throws it again, buy I wanted to check here first.

Thanks folks