2003 Pontiac Grand Prix Code P0128- Coolant Temperature

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

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.

pontiac grand prix


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 (powertrain 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!

Answer: 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, so I'd double check that to start with.

My 2003 runs for about ten minutes then stalls out what can be the problem??
 Could be anything from a vacuum leak, an ignition problem, or most likely a bad crank sensor or ignition module. Any of these would need some diagnosing by a qualified technician. Best of luck.

I have the same problem with my car no heat and runs at 40 degrees could it be plugged heater core?
 If you mean the engine temperature is running at 40 degree, then the thermostat is stuck open and needs to be replaced.

My 02 Grand Prix runs hot had new radiator thermostat and water pump car still running hot and heater blows cold often and occasionally it will blow hot air. What's the problem?
 Could be an internal engine problem such as a cracked cylinder head gasket. Usually it's a bad sign when you have no heat, or it only blows hot occasionally. A shop can do a cylinder leak down test to find out what actually is the problem.

Help! My 2000 Pontiac Grand Prix GT chocked and stalled out, would not re-start. I got P0128 code. Will this code prevent engine from starting or there is other problems??
 No, this code will not prevent your car from starting.

My 2003 pontiac grand prix gt temp gauge goes past half while sitting but goes down as i drive it. There is no smoke or lights on. What could be the problem?
 Check for a restricted radiator or low coolant level.

Hello, I have a 2008 Envoy 4200 Vortec. The Temp gauge in side reads 100 F째 all the time. The A/C Compressor does not come on, But, the fan runs. Is this a bad coolant sensor ?? Can I check it with a ohm meter, if so what resistance should I see at room temp. I am in Arizona so room temp will be a little higher... Thanks for your help.
 Yes, it does sound like the temperature sensor. Just tap on it with a screw driver and watch to see if the gauge jumps around.

I have a 2008 grand prix. The code I also got was P0128 but my temp gauge is reading normal and I have hot air. How do I get this light and code to reset?
 Change the thermostat.

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