P0128 Engine Running too cold?

[Dusty_GMT800]

Got a CEL with the code P0128 saying that my 02 Tahoe is running too cold, I think it may be the radiator cooling fan is running too often, maybe stuck on or something. Does anyone know where the fuse is located? If it isn't this then my other guess is a stuck thermostat.

 

[Rocket Man]

If the fans are electric, you can unplug them at the bottom of the radiator. Each fan has a plug. It could also be the coolant sensor or the thermostat.

 

[Dusty_GMT800]

If the fans are electric, you can unplug them at the bottom of the radiator. Each fan has a plug. It could also be the coolant sensor or the thermostat.

I don't think they're electric, did the 02s come with electric fans? Thought that was a thing on the newer models. My next step is the thermostat, I think it could be stuck open not allowing the engine to heat up enough.

 

[Doubeleive]

02 didn't have electric fans, I think they started using them on some 04's or 05', I would check the coolant sensor first before digging into a bigger job, you could probably just run your heater to crank it all the way up and see if it feels normal hot or just stays luke warm that would probably be the easiest way to go about it, you should be able to tell that way.

 

[Rocket Man]

I don't think they're electric, did the 02s come with electric fans? Thought that was a thing on the newer models. My next step is the thermostat, I think it could be stuck open not allowing the engine to heat up enough.

02's have clutch fans ; I was wondering why you were looking for the fuse unless you did an electric fan conversion like I did. Clutch fans don't have fuses or anything you can unplug but you can check to see if it doesn't turn on until the engine is up to temp. If it starts running before that it's a problem. Then you'd be left with thermostat or sensor.

 

[Doubeleive]

if you didn't add electric fans and it has a stuck fan clutch that could another reason, the fan should spin with some light/med resistance, if it feels pretty tight or doesn't move then its probably bad.

 

[Doubeleive]

02's have clutch fans ; I was wondering why you were looking for the fuse unless you did an electric fan conversion like I did. Clutch fans don't have fuses or anything you can unplug but you can check to see if it doesn't turn on until the engine is up to temp. If it starts running before that it's a problem. Then you'd be left with thermostat or sensor.

beat me to it, lol

 

[Dusty_GMT800]

02 didn't have electric fans, I think they started using them on some 04's or 05', I would check the coolant sensor first before digging into a bigger job, you could probably just run your heater to crank it all the way up and see if it feels normal hot or just stays luke warm that would probably be the easiest way to go about it, you should be able to tell that way.

I run the heat and it's definitely colder than it used to be, I ordered an AC Delco Thermostat on amazon, should be here Wednesday. Also have a couple gallons of Dex-Cool So I'll change out the coolant. I think it may be that the thermostat is stuck open since the truck gets cool when I am on the highway.

 

[Dusty_GMT800]

If the coolant sensor has gone bad, would it not read at all? Or just read incorrectly? If it's a cheap and quick thing to do I'd rather do that before pulling the thermostat and flushing my radiator. Looks like the sensor is about 15 dollars on amazon. This morning my heat seemed warm but not sure if that was just in my head since it was 40 degrees out.

 

[Rocket Man]

You don't lose much coolant changing a thermostat, and it's super easy. Maybe a gallon of coolant, and don't forget new gaskets. You could probably re-use the old ones but why take a chance. Either way.