P0128 code

[ventsyv]

My car throws a P0128 code every so often. After a while the code will go away, but it will pop up again. I suspect the thermostat is stuck open or the temp sensor is bad. Is there a way to diagnose the problem?
The chapter has some specialized tools right? Is there one of those laser temp sensors I can borrow? I can run the car for a while and measure the temperature. If it throws a code but the temperature is in range then I'll know its the sensor.

[mcoupemindy]

What code reader are you using to get the code?

[glindsay]

What code reader are you using to get the code?

And what car do have?

[ventsyv]

2003 330ci. I went to Autozone and borrowed one of their scanners. Its some kind of generic ODBII scanner - I think Actron or something of that sort.

[Uber-Goober]

P0128-Coolant thermostat below regulating temperature. When that came on in my car the thermostat had to be replaced, and judging by the age of your car you probably got the same thing going on. Changing a thermostat may not be all that bad on your car, but unless you know how to bleed it right, take it to a shop.

[ventsyv]

I know how to bleed it, I did coolant change when I changed my water pump.

[prentissra]

I had to replace mine two years ago. Its not that bad unless the thermostat is rusted onto the block.