ICE POSSIBLE DISPLAYS, WHAT IS THIS - 1999 Cadillac DeVille

start with a possible dead battery

ICE POSSIBLE
The instrument panel cluster (IPC) illuminates the ICE POSSIBLE message in the DIC when the outside air temperature drops below 4°C (39°F). The IPC receives a class 2 message from the body control module (BCM) indicating the outside air temperature.

The first thing that should be done ,is to have a factory or professional scan tool hooked up , an check for DTC'S - diagnostic trouble code's . All the modules on the vehicle . Shorted sensor will cause a no start condition , will bring down five volt reference circuit in the body control module . This would cause no communication with the PCM - engine computer . Do you know what serial data network is ? Your best bet mite be to take it to a qualified repair shop .

I assume you mean a external temperature warning light. If so, It means to be cautious as there could be dangerous ice on the road.

THE MILKSHAKE IS CAUSED BY WATER ENTERING OIL LOOKS LIKE SOMEONE WILL BE REP;ACING ENGINE SOON. .DID IT RUN HOT?

This comes on when the outdoor temperature is near freezing to warn of possible ice on the roadway. If it is not 35 degrees or below, the sensor may be defective.

ice, the ice has no limits, on effects.
what does this mean.
doors close down my guess is the latch is jammed, right, in the door jam.
the latch, heat it up with a heat gun and lube it when dry.
park in doors? a garage? if not possible
learn to lube up the parts. so ice can not jam them.
or get help from any mechanic.
he knows what to do, let him/her.

your car is equiped with an outside thermometer, all the light is telling you is the tempture is low enough for ice to form on the road way ond bridges.

It says "ice possible" when the outside temp reads 32degrees or under. Its basically just a warning that its most liekly nasty out.

Well, it might seem obvious but you need to input the code which on my Volvo 850 is a four digit number. I'm assuming this is a used car, so you need to get the code from the previous owner, or if this is not possible, contact the manufacturer directly to see if they can help you. Good luck.

I do not see a separate fuse for the heaters, so you have power thru the 25 amp breaker. You will, have to pull the panel up or access the mirror connector to trace power to the elements. Not sure which is easier. I have pasted all of the relevant diagrams.
Likely failure modes are open heating element and failed heater switch.