Problem with my 2003 Pontiac Grand Prix check
Engine Soon P0128.
Recently had engine cooling system flushed and
coolant replaced.

Question :Just as my car turned over on
170,000 the
check engine light came on. I had
AutoZone check code. Came up p0128. Light
stayed on for about 50 miles then went off. Any
ideas as to what this might be...or should I just
leave it alone until it comes on again? Why does
this come on. Thanks a bunch.

This code is described as 'coolant temperature
below thermostat regulating temp or threshold'.

A common cause for this code is a sticking
thermostat. The coolant temp is too low for
longer than the pcm(computer) expects. It is
possible that there was an air pocket in the
system after the flush and that caused the code.
Keep an eye out for the light to come back on,
coolant temp gauge (if you have one) to stay low,
poor heat from heater/ac system, or coolant fans
under the hood stay on with car off. If some of
these things occur, then have your thermostat
changed, and make sure the system is bled of
air after re-filling the coolant.
2000 Pontiac Grand Prix 3.8 V6. Heater core flushed, hoses all
checked all warm-no blockage, thermostat changed-radiator
checked-cap replaced- Question = I have a 2000 pontiac grand
prix GT-- I all of a sudden have nothing but lukewarm heat at best
blowing. Also my car always runs at 210 but now doesn't get even
close to that. We replaced the thermostat, had the radiator
checked and cap replaced. The heater core has been flushed and
hoses checked all fine. My husband said it heats up when sitting,
but as soon as I drive it, well the temp goes down. My husband
has checked everything he could think of with the heating system.
Can anyone offer any suggestions? I'm one step away from taking
it to the dealer. Which I'm sure will cost me a bundle! Please help!

You need to make sure there is not an air pocket in the cooling
system. That will cause the temperature to be erratic. Also, are you
sure you installed the correct thermostat? If it is incorrect or
staying open all the time the car will not heat up to operating
temperature and you won't get much heat from the vents. You
probably do not have a radiator, heater core, or hose problem
since the coolant temp is not getting to 210 like it used to. It
sounds like a thermostat issue, I'd double check that to start with.
Pontiac Grand Prix Code P0128- Coolant Temperature

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