Cadillac Repair Questions? Ask a Mechanic for Answers ASAP
My info is somewhat limited on your model here but I had seen no one else has responded and would like to see if I can help here.If at any time you feel that I cannot help with this please let me know.
The first thing that needs checked here is to see if the coolant level is low in the coolant reservoir/radiator.If found to be low this will cause all of the issues here and this indicates that there is a coolant leak that needs to be located and repaired then the coolant refilled to correct the faults here.
In some cases this will require a coolant pressure tester to test the coolant system to locate the source of the leak and in a worse case scenario coolant dye is added to the coolant and the engine run for a few days then a leak detection black light used to locate where the dye is leaking from as this would be the leak needing repaired.
It does sound like you are low on coolant with the leak needing located and repaired then the coolant refilled.
I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.
If the coolant level is o.k. it is possible engine coolant temp sensor is sending a false signal reading causing the heater and ac to be inoperative as well as the no coolant gauge and engine hot message.I have seen the coolant temp sensor fail before in the past needing replaced for this type of fault here as well.
This will have to be tested further to be sure using a scan tool that can read the temp sensor signal plugged into your vehicle and some electrical testing then this sensor replaced if found to be at fault.
Let me know if you need anything else and feel free to rate my help here.