My wifes care has this issue. First the coolant level sensor started going intermittent, then the coolant temp sensor started. I replaced both 2 weeks ago and both are still intermittent. There has to be a bad connector or something somewhere, hard to find.

 

I have a 2007 Saturn ion that the temp gauge on the dash is not working I have already replaced the thermostat and the ECTS and when I disconnected the battery it all was working good and then the gauge went out again.... I have read through some of the posts in this forum about this issue and I saw something about the coolant tank has a sensor also !?!? I didn’t now that what I do need to know is if the sensor in the coolant tank will cause the check engine light to come on.... I do have heat and ac works fine but the temp gauge won’t work.... any suggestions?

 

Coolant tank sensor will flash coolant on the display when its bad. Thats just the level indicator.
start tracing wiring. Something is nicked somewhere

 

SES light on?

Go to AutoZone or similar and get codes read for free. Post the codes Pxxxx where x is a number, NOT what the AZ person says they mean.

 

I to have coolent light on dash, temp gauge drops below line, and ac does not blow cold air.I have had this problem for a couple years now. I disconnect battery for few seconds and it all works as normal umtil next time might be 20 min might be couple days. I have replaced sensor on motor, the reservoir tank witch comes with sensor built in,(dumb idea) and thermastat a couple times with no improvement. No one seems to know what the problem is. Everyone tells you to replace thermastat, tank and sensor, and sensor on the motor but that doesnt fix problem.The car doesnt heat runs fine and i never have to add coolant. 😡

 

Some one also said something about transmission oil runs through tank built into radiator and could be leaking mixing the two causing it to have these problems. I would think you would notice it on the dip stick or in the reservoir. I havent noticed it in either.

 

I don't know about Vues, but I DO know if the trans fluid was mixing with coolant, you'd definitely know it by your replies. Good luck with the Vue. The more I read about them, the more I know I don't want one.

 

It's an Ion.
1) What color is the coolant in the expansion tank?

2) Have someone put a code scanner on it.(not just a code reader)
The body control modules control most everything on the car except the engine stuff.
This includes the dash. With seemingly random issues fixed by "rebooting" the car's computers, this may be a BCM issue.

Does the coolant light come on at exactly the same time the temp gauge drops?

 

I am having this same exact issue.

 

Per my comments above, see if you can get a hold of a true code scanner and not a code reader. Code readers will give you only the powertrain diagnostic trouble codes, Pxxxx where the x s are numbers.

Other modules in the vehicle throw error codes which are stored in the car's computer but these errors do not light up the service engine light. To read that these codes, you need a true code scanner.

You're looking to have body control module scanned for codes. This may indicate what is behind the drop in the gauge reading. The gauge is likely reflecting actual behavior or shall I say reading of the sensor from which temperature is inferred. It seems as though the calculated temperature gets sent not only to the PCM but also to the BCM and is used for multiple things. For example the temperature gauge and, by inference, there seems to be a default behavior built into the logic that controls the AC.

If the sensor is temporarily going open circuit or the wiring 4 that sensor loop is going temporarily open circuit, that corresponds to and inferred temperature reading of -40. The climate control system programming in the BCM probably has a lower temperature limit below which the AC cannot be engaged which also means it will be disengaged if it is receiving a reading below whatever the limit is.

The other possibility is that this is not related to the actual temperature sensor circuit but may actually be an internal issue with the BCM losing the signal being fed to it. I would think it updates every so often everything on the dash. However if it loses its data then the signal going to the temperature gauge will likely go to zero. Pulling the fuse resets BCM which then works just fine until the BCM memory gets somewhat scattered.

As multiple people have indicated above, they changed coolant sensors, thermostat, excetera and it just does not solve the issue.

Which is why I now believe this is likely a BCM related issue. The BCM drives the dash. The temp gauge is on the dash. The reading for the temp gauge should directly correspond 2 the inferred temperature data that the BCM receives as a function of time. If that is not occurring, either the BCM is not getting the data are the PCM is getting the data but is not processing it properly which leads to other side effects.

There are decent code scanners that are blue tooth based andtand of vourseccourse code scanners. For a little over $100 you can get a very nice set up on the Bluetooth side. I don't own a corded scanner so I have no idea what a decent one costs nor brands to stay away from.

Or you can take it to a trusted shop and cough up the $99 for a diagnosis. Some service folks will freely give you the codes, some will hold them hostage, so ask up front if they will provide you the codes or you will be no further along.

Let us know how it goes.