Check engine light for low coolant temp?

[CrackRabbit]

Was driving home last night and had the check engine light pop on on my 03 Focus.
Got the code checked today, gave me P0128: Coolant temp below thermostat regulating temp.
The car does tend to run cool on the highway, but is fine in traffic and has never overheated.
Am I looking at a thermostat that is stuck open or possibly another issue?

CrackRabbit

 

[sjwaste]

Stuck thermostat is a good guess as a general problem, but I know nothing specific about the Focus. I'm not sure how the engine bay is laid out, but that's one of the cheaper fixes. Have you googled it to see if it's common?

My Supra used to take a while to warm up, especially in the winter, b/c the thermostat was stuck open. Replacing it was also a good occasion to change the coolant, since it had to be drained anyhow.

 

[bruceb]

Sure sounds like a classic case of stuck open t-stat.
May as well change it and the pressure cap and depending
on the age of the coolant and it's condition, a cooling system
flush should be done.

 

[boomerang]

I know it's the wrong season, but turn the heat on and see how hot it's blowing. What's the temperature gage showing?

Thermostat stuck open is a good educated guess, but it is possible that it's just a bad sensor.