p0128 code/Service Engine Soon

2003 gmc sonoma ZR2 Highrider 4.3 vortec V6: I have searched threads and have not found any answers....lil help here

P0128 - Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)
I just added coolant to my zr2 and the temp is runing around 160+- when it usually runs @ 240+-.
Is it safe to drive if coolant resivior is full?
How do you clear this code?
Do I need a new Tstat?
Does it need to be cleared by a shop computer?
Is it hard to change, if you are mechaniacally inclined)
I just disconnected battery terminal and code did not clear.
any help is much appreciated!

Matt

so you had to add coolant to it? and how low was it if you did? if it is leaking then you need to find the leak and fix it. the truck should run about 200-210F. if it doesnt then your thermostat is probably in need of replacement.

2003 gmc sonoma ZR2 Highrider 4.3 vortec V6: I have searched threads and have not found any answers....lil help here

P0128 - Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)
I just added coolant to my zr2 and the temp is runing around 160+- when it usually runs @ 240+-.
Is it safe to drive if coolant resivior is full?
How do you clear this code?
Do I need a new Tstat?
Does it need to be cleared by a shop computer?
Is it hard to change, if you are mechaniacally inclined)
I just disconnected battery terminal and code did not clear.
any help is much appreciated!

Matt

Well you can ussually have auto zone erase a trouble code after they read it. When you added coolant did you purge the air out of the coolant system by running the engine up to normal operating temperature with the radiator cap off (some vehicles use a cap at another location in the coolant system for purging air) and make sure you have the heater on to purge air from the heater core.
You can also have a bad coolant temperature sensor, I am not sure where the sensor is on your engine but you should be getting a 5 volt reference to it, and maybe someone on here knows the resistance values it should read at specific temperatures, 160 sounds a lil cold maybe thermistat if the temperature is actually that cold, but 240 sounds a bit hot it may be a sensor

I have a 2002 4dr LS 4wd ZR5 S-10 with the Vortec 4.3L V6. The Service Engine Light came on. I had Auto Zone read the code (P0128) and then clear it for me. It came back almost right away. So I changed the thermostadt (Napa $6) and add a Standt radiator cap. I then drove over 350 miles round trip to Chicago with no problem. The temp needle is sitting between 200-210.

Coolant Temp Below Thermostat Regulating Temperature
a normal regulated temp for thermostat is right around 192 degrees. If it is below the regulated temp, the thermostat maybe stuck open, which doesnt allow the coolant to get warm because it is being circulated even when the engine is cold.

hey mine is doing the same thang but my ? is where is the thermostat located at so i can replace it? its a 2003 ZR5 4.3l 4door 4x4

Old thread here, about to be closed, but it should be in the upper hose housing. If not, repost a new thread, thanks.