P0128 Coolant Thermostat Malfunction

Hello everyone, im a newbie on here posting, but have been browsing the forum for sometime now.

Wifes truck just through up this P0128 Coolant Thermostat Malfunction code and was wanting too get some input on it.

2005 X5 3.0i with 96k on it. runs fine and doesnt run hot, runs in the middle of the temp gauge and never moves past the middle. has plenty of coolant and has been kept up.

let me know what you guys come up with as far as info i need or whatnots.

thanks

If this were mine, I'd replace the thermostat, the water pump and the expansion tank. Unless you know these have been replaced recently.

Does it take a little while for the temp needle to raise to operating temp? Did your temp needle move to the left (11 o'clock position) when you're on a hway? If so, you have a fail-opened thermostat.