P0189 code

My 2002 Oldsmobile Intrigue has been throwing a P0189 code. When I look it up in the book that came with my code reader is says that it means the engine coolant temperature is too low. I clear the code but then the Service Engine Soon light will come back on about a week later with the same code. There are no driveability issues at all and the car seems to be running in the normal temperature range, maybe a little less. Could this be a faulty sensor or is something else going on?

Not much on that code except:

P0189 Fuel Temperature Sensor B Circuit Intermittent

Actually I mistyped it; it is P0128. I am assuming that either the thermostat or coolant temp sensor is at fault. Since they are both pretty inexpensive I am going to replace them and see if that solves it. Thanks for the response.