P0128 coolant temp low 2001 grand prix 3800 series 2


Driving home from work yesterday my service engine soon light came on and stay’d on. I has been very cold recently in NJ. I parked the car and popped the hood. The fan was running even thought it was a cold night and the temp gage was slightly below normal. When I statred it up the fan stayed off but the light is still on. Noticed the same thing this morning. I took it to advance auto parts to get the code read. It came back P0128 coolant temp low. The SES light was reset and didn’t come back on yet. I think it might be ok because the fan does not come on and the coolant temp seemed to be higher today.

Also I replaced the dexcool with global in October. Could the dexcool have gunked up the system causing a faulty sensor?

Autozone said it could be a thermostat stuck open or a bad sensor.

Thank’s for you’re help

This illustrates why having the code can make a difference. The code P0128 reads, "Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature). That says (to me), that the engine isn’t hot enough to cause the thermostat to open. Why isn’t the engine hot, but, the engine cooling fans are running? The cooling fan relay may have stuck closed from the cold. Maybe. When the engine is cool, check the antifreeze level in the radiator (not, just the overflow bottle). Fill the radiator, and fill the overflow bottle to about 1/2. If the coolant level is down, have it checked for a possible coolant leak.

I’d replace the thermostat and possibly the coolant temp sensor, in that order.

Hellokit has a good question; Why are the fans running if the coolant temp is too low? The fans have their own temp sensor, usually in the radiator. How is the radiator getting too warm if the engine is too cool?

When the dexcool was replaced, did they THOROUGHLY flush the cooling system? What does the coolant look like, now, when you open the radiator cap?

Is your heater working well?

I seem to be only able to losen the radiator cap and turn it can’t get it off to take a look. Before I got it flushed I noticed a lot of sludge in the overfill tank. I don’t see that anymore. The mechanic said it was a real mess when he changed it and got it as good he could for now. Reccomended I do it again in the spring and show’d me how to do it. Also my heater works fine.

I have driven the car 3 times now since resetting the light. All trips 20 minutes or less. Everything seems normal the temp is at a higher range. When I park and check the fan it is not running. mabye the problem won’t come back for a while.

Thanks for everyone’s help

Was fine today to work and back 30 m each way

When you want to remove the radiator cap, you have to push DOWN on the cap as you turn it. Sometimes you have to push down rather firmly while turning the cap.