My check engine light came on yesterday about 15 minutes into my commute home. Stopped at Auto Zone and they pulled the code P0128. They paper they gave me states:

Definition: Coolant temp is always low.
Explanation: The powertrain control module verifies that the engine is at proper operating temperature.
Probabale cause: 1.)Check coolant level. 2.)Thermostat defective. 3.)ECT sensor defective.

According to the trouble code list that Wayne added to the site it states: DTC P0128 Coolant Thermostat.

I didn't get a low coolant light, the temp gauge shows it in the same range that it's been in since I got the car in July, actually for some reason when I installed the CAI it seems to run a little cooler but the weather also started to get cooler around then. The coolant in the recovery tank was in the normal hot range.

OK so I'm thinking... (insert your own joke I'll wait...) I was going to go a head and flush the system when it started to warm up but looks like I need to do it a little earlier. I'm assuming replace the thermostat and the sensor just to be on the safe side. Correct? Opinions?

Thanks in advance for any and all help

 

I would replace your thermostat and flush the entire cooling system, then go from there. A new t-stat should fix it.

If your car is running a bit cooler with the CAI, sounds even more like the t-stat. If your t-stat was working correctly, it should be adjusting whatever way it needs to so that the car runs at regular operating temp.

 

Wasn't running much cooler, maybe one "hash mark". CAI was put on early in October so it's been almost 3 months.

That's about what I figured thermostats aren't that much and Auto Zones web site list the sensor for something like $13... While getting into I might as well do the whole job.

 

...Hi Brian, CAI can send codes when the weather gets colder..., but I think it's better 2 be safe then sorry or broke down on a road somewhere.

If you have the $'s, I would make the investment in your AweSome SS.
Has your Radiator ever been flushed ? Is it the original Thermostat ?
If so, U R due 4 a update : )

Keep us posted & Good Luck 2 U & your Monte : )

 

Didn't realize that a CAI could throw codes in the cold... Don't think that is the case though it has been colder... MUCH COLDER!

I'm thinking the $ shouldn't be too bad that's why I'm asking here figured with the experts on this site I'll get the best info.

I'm not the original owner of the car, just got it in late July. Was planning on transmission and coolant/antifreeze flush but wanted to wait until next spring for both (the car alone put my finances in a bit of a shock). The PO had installed a K&N drop in filter and I think (by the temp guage) he/she may have put in a cooler thermostat too but unsure of that and if the radiator was ever serviced. I realize it probably needs it so I'll have to jump on it when the cold front lifts. My mom wants me to take her SS to work for a while so it can "stretch it's legs" (she doesn't take it out that often and when she does it's usually short city drives)... Can't say no to driving an '08 Impala SS when someone ask!

 

So the coolant on your SS was never flushed??? It's possible that it's starting to gum up and not flow so great. I would definitely get it flushed.

I was having issues with low coolant lights, when my coolant wasn't even low, so I was going to change the sensor but I wanted to do a coolant flush anyway and that fixed it. Dex-cool is crap and can cause issues. Shouldn't cost much to get it flushed... maybe cost me $30?

 

Check to make sure the thermostat is not stuck open. The coolant temp sensor for the computer could also be defective. basically the the coolant temp has to get up to 175 or so degrees to go into closed loop operation. If its not getting there or the computer doesn't think its that warm, it causes the code.

 

is there a additive you can use instead of a flush, or is a flush the best option after a t-stat?

Also is the o-ring for the t-stat re usable, since no one seems to stock them, i can get the stat all day long but not the oring.

 

I just got that code as well, I went to an auto parts store to get the thermostat, but the one they pulled out did not look like the stock one, so I went to the dealership and got the AC DELCO thermostat, #1 it comes with the rubber gasket, and #2 it is way differnet than the one from the auto parts store (off set and with some sort of bypass or something *I am sure it is there for a reason*), I would not be cheap on this, it was about $17 at the dealer vs $10 at the auto parts store, for $7 it seems well worth it, if you already bought one take it to the dealer and compare, I am sure you will want to return the generic one and use the AC DELCO thermostat.

 

If the thermostat was replaced with a 165 deg piece it will throw that code. What does the temp gauge read? Anything under 170-175 will throw a code. Replace the t-stat with a 180 if S/C or a 195 t-stat if N/A.