How to get the check coolant light 2000 Cadilac Deville

If it's just one door, check the door switch.
If the lights do not work regardless of which door is opened, check the "INT LP" relay in the rear fuse block (under rear seat). Unfortunately, this relay is controlled by the Rear Integration Module (RIM) based on input signals from the doors etc. If the relay fuse and relay are ok, then you may have to replace the RIM - check the car error codes (DTCs) first to make sure.

There is no way to reset the light , you probably need a new coolant level sensor !
Coolant Level Sensor Description
The coolant level sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is located at the base of the radiator surge tank and is not serviceable.
CHECK COOLANT LEVEL (2)
The IPC receives a discrete input from the engine coolant level switch. The engine coolant level switch is normally closed. When the engine coolant is low, the engine coolant level switch opens. When the IPC receives an open signal from the engine coolant level switch, the IPC displays the message on the DIC.
you have to replace this ,Radiator Surge Tank !

Do basic troubleshooting. Spark to plugs? Fuel pressure correct? Injector pulse?

Does the VAT have to be reset?

Sir if the check engine ligh is flashing that indicates a PO300 code which is a missfire code. To determine which cylinder you will need a scanner to find out. The problem could be a failed sparkplug, a failed ignition module for that bank, a failed injector. At any rate it will require trouble shooting to diagnosis. Wish I could help more. Thank you

YOU MAY HAVE A BROKE SHIFTER CABLE

HOW LONG DOES IT TAKE FOR THE MESSAGE TO COME ON? CHECK FOR SMALL LEAKS IN HOSES GOOD LUCK

Is it the LOW coolant light? Your car is equipped with a sensor on the expansion tank (radiator overflow). Right front fender. It's there for when the car heats up. As the engine heats up and the coolant expands it racks into the reservoir/overflow/expansion tank. When the engine cools, it sucks the coolant back in. If your car was low on coolant then there's a good possibility that as it cooled, it sucked the recently added fluid in. Check that it is full to the "cold full" level by looking at the tank before you start it for the day. If it's not, then the sensor is telling you to add coolant. If it is, then the sensor in the tank may be bad.

IT MEANS THAT A FAULT HAS OCCURED IN THE SYSTEM AND THE SYSTEM HAS BEEN DISABLED, TO FIND THE FAULT YOU MUST HAVE THE DEALER TEST IT FOR THE TROUBLE CODE THAT IS STORED WHEN THE LIGHT STAYS ON.

the problem could be the engine coolant tempature sensor. all1992 through 1994 models equipped with electronic climate control can display trouble codes.replace coolant temp sensor.if problem contines have powertrain control module checked