You may take good care of your car, keeping the radiator clean and the coolant tank filled al the time. All of a sudden your coolant light turns on but the tank is full, what could be the possible causes? Some people will drive around with the light on and just ignore it, keeping constant vigilance on the level of the overflow tank, however this is never a good idea.


The coolant light will come on when the sensor senses an incorrect change in the temperature in your car system. Typically the sensor, which monitors the coolant temperature, knows how to adjust to different temperatures depending up the status of your vehicle: running, warming up, or cold. The sensor is very vital because your car’s systems depend upon it running at prescribed temperatures. The coolant sensor is also termed the master sensor.


Your sensor may get bad or it may simply give a bad reading. A bad coolant sensor may create a decrease in fuel efficiency or it may also cause the vehicle to fail an emissions inspection.

It is likely that the problem may be a loose, corroded, or faulty link and not a problem with the sensor itself. Have all of your links and connections checked to see if this may be the cause of your problem.

Visual diagnoses can sometimes indicate a problem with the sensor. You will be able to see if it is cracked or badly corroded. In this situation, removal and replacement is required. More often, though, you will be required to take voltage and resistance readings from the sensor to see if it is working properly.

If your car is older, the sensor has worn with time and may be failing but not entirely failed. It is not a bad idea to keep a check on your sensor’s readings. Changing a sensor that is beginning to show extreme signs of age and wear can stop future problems.


You may have some sensor issues that stem from the thermostat rather than the sensor. Your thermostat may get stuck open thus causing improper readings. If you recently had your thermostat changed, check to see that it was replaced with the correct size.


The coolant light might be signs of a more major engine problem. When you notice a crack in the block or the intake gasket you will leak coolant and oil, usually slowly initially. You may not observe the difference at first, thinking that your tank is full. A repair to a cracked engine block or head gasket is an expensive one. While you drive, note if you smell coolant. That may be a signal of a leak that you haven’t seen yet. Also check below your car for any telltale drips.


Your issue also be a faulty coolant level module. Check the wiring to be sure nothing is loose or worn.


You may want to get your vehicle to a qualified repair location to diagnose and repair your problem if you can not easily diagnose it  by yourself.