My car is doing something strange :

The coolant sensor will show : Coolant Temp : --- C

Means he doesn't know the temperature of the car, the fan will run at his max speed... and then suddenly after 1 or 2 days, the temperature will start showing again the fan will stop and everything is back to normal.

Does anyone have or had this problem? and by the same time, can somebody tell me where is the coolant sensor on the car?

 

i have the same issue i was going to post this up today lol i was told it is a fauly sensor but then it starts to work so ya someone shed some light on this

 

Awesome I'm not the only one having this problem so this means there is certainly someone who will explain us what's wrong!

 

ya exactly just keep bumping it til we get an answer

 

you could always try cleaning the wire connections of the sensor, otherwise it sounds like a faulty sensor like mentioned.

 

ya i was going to replace mine next week and see if it gets any better but where is the sensor located i will try cleaning it

 

this is per the Haynes Repair Manual for 05-07

"...the ECT (Engine Coolant Temperature) Sensor is located at the right front (passenger's side) corner of the cylinder head on 2.0l engines, near the valve cover. On 2.2L and 2.4L engines, the sensor is located in the thermostat housing, between the two heater hose pipes..."

 

But a faulty sensor would cause it to work and then suddenly stop working, then coming back? I got this problem since last year lol... It was okay for 6months straight but now it started to bug alot

 

I duno...but the sensor on GMpartsdirect is only like 16 bucks.

 

It's probably the thermostat b/c I have the same problem. I used my interceptor to "clear" the codes even though there wasn't one at the time and it immediately started giving a temperature readout again instead of "---". I haven't got around to changing it yet. In my particular case, I believe mine is stuck open because sometimes it will take a while to warm up. I first noticed it in the spring time. Mine was fine during the summer until recently when the weather started getting cooler at nights. Thats what would trigger mine. I could also still get a temperature readout on the interceptor scan gauge even while on the DIC, it showed "---". So, that leads me to believe its not the sensor but rather the thermostat.

 

Even with a stuck open thermostat the coolant sensor should still give you numbers.... It would give you the air temperature instead of the water temperature

 

Yes, it should and it could give a temp readout. However, this is apparently what the computer does if it doesn't get to the desired temp in a set amount of time. It turns the temp display to read "---", turns the fans on high, and i think it may disable the a/c.

If you do a search, theres a couple threads on here. Here's one of them. There are a few threads that debate on what the problem is.

https://www.cobaltss.net/forums/prob...play-c-223905/

Like I said, I know for sure mine is the thermostat. Because, It can take a while to warm up sometimes. As soon as it would reach 160F, it goes to "---". So in my case, since I have access to a scan gauge to reset it, and the readout comes right back on without touching anything I know its not wiring or a sensor.

 

Alright so these guys are debating on changing either thermostat or coolant sensor. Tomorrow I will order the coolant sensor because in my book, it would be the sensor that is malfunction. However I will post if this fixes it or not.

My car says ---F as soon as I start it, and correct me if im wrong, the coolant sensor should read a temperature even with an open thermostat. If it's showing no temperature then it means the sensor reads something that is totaly wrong and the cpu wont accept it, so does not take care about him anymore, starts the fan at high speed by default.

 

Coolant sensor or short in the circut. Our coolant temp sensors (at least on the LSJ, i'm assuming the LE5 is the same design), are falling resistance. As the temperature increases, the resistance in the sensor goes down. I had a wire shorting out in the harness, causing the coolant temp to shoot up dramatically to max or blank out when it made contact with the intake manifold. Was worse when wet. I replaced the sensor and didn't change anything, then a buddy of mine found the wire worn through, ziptied a piece of hose around the harness at that spot, never gave a problem again.

 

Aye but my goes crazy and come back to normal so i dont think its a worn wire

 

That's what mine did, would jump up and go blank, then go back to normal.

 

Change the thermostat and it will be all fixed. I had the same issue the thermostats rubber gasket is getting eaten away by the damn corrosive dex cool . I also went with green coolant rather than the orange (dex cool) this time.

 

One day I was driving, and I looked at my sensor... My car said 298. I immediately thought "Oh ****". Then It went from 298, to 124, to 250, to 150, to ---.

I went to autozone, bought a replacement sensor.

On the 2.4, its located BEHIND the block, driver side, has wires connected to it (obviously).

Caution: Don't change it while your engine is hot. (You will get burned)

Now, I had to replace it twice. Because, the 1st time I changed it, it did the same ****, except it just stayed at --- from the get go. I think I got some wires wet or something.

Replaced it AGAIN, this time, I disconnected the battery, and was VERY careful about not letting any liquid get in the connectors.

Voala. It worked like a charm.

 

My cobalt was doing the same thing as all yourguys cobalts are doing...was driving me crazy...so I changed my t-stat and everything works great no more problems..its not hard to change..hardest part was gettin the air out of the system....change your t-stat

 

ya i am doing the thermostat this week end how do you do it exactly

 

Okay so I've been thinking about it alot the past days and told myself maybe I was wrong. The temperature of the car didn't seem to increase fast so I think the computer says it's not normal and just stop listening to his coolant sensor. The car does not get to his temperature since the thermostat is opened and let the coolant go into the radiator. So I bought both thermostat and coolant sensor and replaced the thermostat first. It's been a week now and I didn't get the problem anymore so I will just send back the sensor.

The thermostat wasn't that easy to change since there is a bunch of crap in front of it. But in fact, changing a t-stat it's not a big deal, I removed the 2 bolts, raised the hose so the coolant didn't leak all around. Removed t-stat and placed the new one. Put back the hose with bolts on, start the car, open the tank of coolant and fill it up(since some liquid leaked on the floor), let the car run a bit it'll eat the coolant so the tank gets emptier, refill it. Let the car cool up and fill it to it's limit.

Don't do this while the car is hot you'll get burned. You have to leave the tank opened so the air goes out and let the car run to high temperature so the thermostat opens itself.

You can correct me if I'm wrong at some point, but that's what I did and it worked.

 

your rite but i drained the coolant first from the radiator...so i didnt have a big spill on the floor....car needs new anti freeze in anyway..plus the reason why the t-stat was bad is from the dex-cool eats away at the rubber gasket in the t-stat and holds it up from closing...

 

Right but I still needed 4L of new coolant ! I sucked at making it not leak...

 

ive been getting the weird coolant temp but i believe its soaking heat from my turbo and exhaust. only does it after hard runs or if the car is running for long periods.

 

Had that happen on a 2.4 with a turbo kit. Need to command the fans on earlier, otherwise it gets hot and stays there after some hard driving.