I had this problem with a 2007 Chevy Cobalt. I changed the coolant sensor and even though the check engine light went out I still had a reading of "---" on the coolant gauge. The problem is most likely one of three things: a low coolant level, a bad coolant sensor, or the thermostat needs to be replaced. The only other possible thing it could be is a bad BCM (Body Control Module) which in that case you would most likely be having other weird problems.
The Thermostat and the sensor are both very easy to get to and replace. Take off the engine cover by removing the oil cap and they are both to the rear of the engine on the driver's side. They are right next to each other.
Hope this helps!
You will need a code reader,auto zone can pull the codes for you for free,the coolant sensor tells the computer the temp,and computer activates the cooling fan relay,with ground,the ac being urned on,should start the fans,it may take a while after turning the ac on.Check coolant sensor,and thermostat can be stuck closed and the sensor will never read the hot water.
I had the same problem with a 2007 Chevy Cobalt. I changed the coolant sensor and even though the check engine light went out, the reading still showed "---". When this happens its either a low coolant, a bad coolant sensor, or the thermostat needs replaced. The only other thing that it could be is a bad BCM (Body Control Module). In that case though you would most likely be having other weird problems.
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FIXED. I changed the sensor, both fan relays, the thermostat and all the coolant. It's been a week now. No issues.
Took positive battery cable and touch it to the negative side for 3min it worked for me don’t know how long but it’s working now
You have to bring it to your garage/mechanic. They will hook the car to a scope and read off the fault codes. That is how you will know where the problem lies.
A DTC will be set if an abnormal reading occurs, P0116 for sensor performance, P0117 low input or
P0118 for a high input. The coolant temperature sensor temperature reading should closely match the
air charge/manifold temperature reading on a scan tool if the engine has not been run for over an hour.
The sensor circuit can be checked for proper voltage using a voltmeter.
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