Low coolant temperature code 2008 Ford Ranger?

I have a 2008 Ford Ranger XL, regular cab, short bed, 4x2 with over 203,000 miles. Around a yr ago the check engine light came on with the 0128 low coolant temperature code. No performance issues at all, fuel economy is the same. Temp gauge gets to a "normal" level between cold and half. A/C and heat work great. What could be the possible issues causing the code? So far all I've read and heard is thermostat is stuck open, truck heats to normal level just as it always has. Could it be thermostat or cht (cylinder head temperature sensor)?

If it reaches and maintains the proper temp, I wouldn't suspect the thermostat… I'd suspect a bad sensor.

Thermostat maybe opening too soon or stuck open making the engine go into closed loop for a longer time. Replace the thermostat with a factory one. No joy, see a mechanic with a scan tool to verify coolant temp sensor operation.

You need a new thermostat.

Bad thermostat.

If your motor doesn't reach operating temperature with in 3 miles of driving I'd start with a new thermostat. Stant makes a good after market thermostat.
The coolant temp sensor is working properly if the temp gauge is reading right. You may want to hook up a mechanics scan tool to monitor what the PCM is seeing for coolant temperature.