my fan is always on and my coolant temp is blank and my a/c wont turn on cause of this.

you are not alone--- have 07 4-door for last 3 years- in last six months the coolant temp dashes out (---) and the a/c wont come on- some times i get numbers back and the a/c works until the display dashes out again-this also kicks on the check engine light- had the trouble code checked and was told it was coolant temp below norm- changed the engine coolant temp sensor ($25. & 2hrs my labor) worked great for 3 days and then display dashed out again and has stayed that way-checked haynes manual wiring diagrams- both the a/c and the temp sensor feed into the engine control module- checking this means taking it to chev auth service center which means lots of cash- my next step is to change the thermostat ($8.) THIS IS THE MOST STUPID THING I HAVE EVER HEARD-WHY WOULD THE ENGINE COOLANT TEMP KEEP THE A/C FROM WORKING- THANKS CHEVY- sorry i don't have the answere yet- if you get one that works please post it - i will do the same-- good luck

im having same problem with my '09 cobalt now. has anyone figured out the resolution??

Having the same problem with my old lady's parents car

I have the same problem! 2007 4dr sedan! I have changed the Egine Coolant Temp. sensor twice and still about three days and then it goes out again. Still dont understand y the A/C goes out? Any luck anybody please let us know....

I had the same problem too, it turns out the thermostat needed to be replaced.

I have a 07 Pontiac G5 GT, I was on the highway with roadwork traffic going really slow. When I looked down and noticed my temperature gauge was blank and or reading this ( --- ) and because we were not moving as fast and the noise was down I heard the fan running. I have a 30 minute drive home from work and it remained on the entire way home. I'm thinking it's either the thurmoustat or the temp gauge sensor. But it hasn't thrown a code or check engine light this could also be due to the fact that my internal computer is absolute ass and it's not working properly either.... So I'm at a loss. I guess I'll drive it until it breaks down in my case the fuel lines are already leaking and I purchased the car used about 4 months ago.... I definitely got a lemon on this one.... But if it isn't one of the two things I said of previously then I might just strap a pound of c4 to the damn thing and watch it go!!!

My car is having same problem. I change the temp sensor and nothing has change. I change the thermastat about two months ago. Any answer will help thanks.

I have same the exact same problem in my 2007 cobalt. I changed the temp sensor. Worked fine for a few days and temp went dashes A/C stopped working. Cooling fan runs from start-up. If I unhook my battery for a few minutes, then everything works fine untill my temp reaches between 145°-170° then it Blanks out on the dash, the cooling fan comes on and the A/C stops working. I unhook the battery and it's like groundhog day..I think they need a recall. I'm sure you do too..But that said. If it's below 40° ambeiant temperature outside, It works fine. The fan comes on at 210° the AC works fine. But the engine temperature will drop down to 156° and fluctuate between there and 169°.. If it's 50° outside though​, it will stop working when the engine temp reaches around 150°. Help a fellow bro out please. Do I need a new A/C / Heater controller that goes in the dash. Is it a high low fan sensor. Is it the technology made by aliens, and humans don't have the brainpower to figure it out...Or it's a good little money maker for dealerships, bingo! Yeah I know. Trade secrets and all...

This is definitely the thermostat. Two screws easy fix. On my thermostat is have a seal in it. And I just change mine a month ago I was like there is no way. And yes it went bad. Theses cars are well known for this. Change yours. Put a bucket under the car. Because antifreeze will go everywhere. Change it. And tighten up then add. Antifreeze drive up road until thermostat opens and will fix the problem. I'm a girl. If I can fix it. Anyone can. Good luck.

I have the same issue, ECTS waa replaced along with the thermostat, just had the collectors and pigtails replaced and it lasted 3 days only to stop reading a temp again

I changed the thermostat, worked fine for about ten miles and done the same blasted crap again. I'm at a loss now?

My next step is to Chang the coolant. Perhaps someone has added regular tap water to the system. This could cause a low voltage short as it travels thru the cooling system. Only deionized water ( has all minerals removed that can carry a current) is to be used. Will be a few days before I can try this. But I will post an update when I find out if this works.

I don't have an answer yet either. I changed my thermostat and it worked for about 4 days. When I took the old "fail safe" thermostat out, it was fine and not stuck open like it would have been had it failed. A week later I changed the sensor. It worked fine for a day and a half. Cleaned the connections on the ECM and it worked fine for another day. It's all back to the same dashes, engine light on, no a/c. I'm out of ideas, patience, and money.

Maybe a computer or wiring issue?

Same issue with my 07 cobalt ltz. It’s has 119k and has never had a problem till now.

Ok everybody, I added some Prestone coolant into the coolant reservoir(was maybe 6-8 ounces),and everything works now. Try adding coolant first because if you are just a little low this can happen and makes you think it's the thermostat and/or sensor.

I had this problem on my 2006 cobalt and I changed the relays labeled fan 1 and fan 2 located in the fuse box and it fixed the problem.

So, this is what I'm going to do gathered from all the above. I'm going to replace the sensor, the thermostat, ALL coolant and both of those relays. If I'm going under this car I'm doing it once with everything in hand. If that doesn't work, I will learn to live with it.

So did anyone got there problem solved? I have the same issues with my 2008 Chevy Cobalt

I have the same problem and and OH cobalt I'm going to figure out why this problems going on I believe it to have something to do with the air conditioning switch which under too much pressure will stay locked in on position and as you know when you turn your car on AC the fan runs continuous if this doesn't fix it when I get done with it I'll let you know and if it does I will to

It's the thermostat... Easy fix just drain coolant from plug at bottom of radiator take 2 screws out of the thermostat housing then take out thermostat and put the new one in the same way replace the coolant and your temp gauge will read after a few and the engine light should go off after a full drive cycle after you've driven it once and engine is hot make sure u burp the coolant reaivoire

Replacing a bad Thermostat Cobalt LS 2.2 liter

Even though you buy new some thermostat are bad. Change mine 2x fix it

I’m having same problem smfh 07 cobalt ls. What a peice of shot lol

You got that right. Mine was the gasket to tue thermostat. But now having a problem with it riding ruff. As I have changed everything on the damn thing. Definitely junk. Think god its paid off never again will I buy another one.

I went and bought the new sensor and thermostat which mine was going out but after I did it still didn’t show but I got mine working by disconnecting my battery

I have changed the thermostat 3 times, last one an AC Delco. Also changed the sensor. Works fine for a while then nothing again. I have noticed that the A/C doesn't work correctly and have tracked it down to the blower switch. I will change that and see if it's all connected some how? So tired of GM Pieces of Shit! Was my Wifes car and was purchase before we met. I will NEVER EVER purchas a GM product.....EVER!!!!!!!

Check for loose wire/connector, change coolant, change thermostat, or engine coolant temperature sensor.

When this happens id drive super aggressive for a bit and eventually it would read again, I also noticed that driving too soon after starting the car caused it to read --- again. That's just my quick fix for it I don't wanna put money into it yet because I haven't found the best solution.

Believe it or not it was the damned thermostat, I just replaced it 2 weeks ago when my cooling fan went out and living here in Phoenix I decided to go with the daily safe thermostat, true to its name it failed open and caused the coolant temp not to read, the fan to stay on high at all times and the ac not to work. I used the OEM thermostat this time and had to disconnect the battery for 10 minutes and all if right in the world again. Hope this helps someone

So I've got the same issue (09 cobalt SS) and I just ordered the new thermostat, I'll let you know if everything works, just curious if the fan stays on some minutes (5 in my case) after turning the car off

Please someone who has had success post this is the absolute worst

I've had this same problem the --- in the coolant display, the fans come because the ECM thinks the car is critical, so it attempts to cool the car any way possible. I took a code reader with me (now been in the car for over 2 weeks now), and here is what i've found. 1) the car will start out reading, at about 65 - 69 C the reading will go to the --- thing, so while i was driving with the reader still plugged in, i did a reset (even though it said "no codes found" TA DA ! READING came back, and does, every single time !! So far this is what i've found, will come back to this thread and post a fix once i have one.... THIS HAS NOW BECOME MY SOLE MISSION IN LIFE TO FIX THIS DAM THING !!!!!!

SO! The problem IS the thermostat. After studying the code reader and temp cuage in the instrument cluster watching what was what, went through hell a nd a 1/2 jug of antifreeze, along with a new thermostat, problem IS fixed !

Yeah well I’ve done that too and only a week or two later I was right back where I started.

I've have this same problem. Just started the day before yesterday. '07 Cobalt. Nice get around car but for some reason this model has issues. Last year it was a rusted gas line I had to replace. Read up and quite a few have had the same issue...but no recalls

So I finally found what was wrong with my car (2009 SS), hope this helps someone, I'll just write up the steps I took to reach the answer because I've seen it is not the same issue in every car (Note: if your dash is reading --- coolant temp A/C won't work): 1-. Replace temp sensor and thermostat both ACdelco. Didn't work for me. If this works for you then you're done with your problem, I changed it twice cause there was people who said the second one worked (thermostat). It's your decision if you want to change it once or twice. (Now I have one temp sensor and two thermostats + the ones in the car, should have changed them only once) 2-. So step one didn't work. Next step was to check signal from the sensor to the PCM before changing anything else. If signal it's not correct then probably you'll have to rebuilt wires from the temp sensor to the PCM, get it checked by your mechanic unless you're one. When I checked this the signal seemed to arrive correctly to the PCM, asked a friend to get it checked too cause I'm not a mechanic. Everything in my car is working well but somehow the PCM is reading 64 F constantly until dash reads --- even though the temp sensor signal is arriving to the PCM. 3-. Now that I'm sure it's the PCM I'm gonna open it and check if it can be repaired (probably not) 4-. Change PCM :'( (IMPORTANT NOTE: at first I found a forhum where people claimed to have the same issue bit with 108F, if your car is reading a constant 108F instead of 64F before it gets to read ---, your PCM has a bad ground (as usual with these cars). Just ground it to one of the bolts in the PCM (I know turbo and supercharged SSs have these two bolts, I don't know if 2.2/2.4 have them) I really hope my experience helps all of you dealing with this pice of **** problem. If you have any questions just message me in Instagram: @black_supersport

2008 Chevy Cobalt does not mark temperature

Hello, good morning, someone who helps me in my 2008 Chevy Cobalt does not set the temperature and turn off the air conditioning.

Samuel, replace your Thermostat in the water.

Hello good morning, Thank you for your response I already put the new thermostat and the new temperature sensor and nothing.

Samuel, check signal to the PCM, if signal is good you'll have to check PCM, if it's not good, you probably have a wiring issue