When I turn on AC about 10 to 15 mn the low fuel signal start flashing even though the nidle is at 12 o'clock showing gas tank half full then later will trigger the check engine light. It may stay on for days and turn off itself.... the car still run normal. What could be the problem?

I have the same problem in my 97 V12 but it's not related to the AC and it happens when the gas level goes below 1/4 of the tank. See if you can pull the code, mine showed P455 (Fuel Purge System leak), I haven't done much troubleshooting but for now I keep the tank above 1/4 and all is good.

Flashing reserve light usually means the gas cap is loose, forgotten, or its seal has failed. New ones are pretty cheap.

It could also be related to a biodegradable wiring harness if its a 92-95......

Can you pull the code?

How can I pull the code ??? What to do with it ??
Another things that I experience today, I unlock, open the door and the alarm went off. I never knew my car has alarm, never goes off. I panic and didnt know how to turn it off. I start the car and drove it to the garage. Can you tell me how to turn it off?

What year is your car?

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97 S500 144K
I experienced frequent cutoff when the heat indicator goes up to 80. Base on previous discussions from others, it needs CPS changed. I will go ahead and get it done and see if it will fixe the problem.
Any advice?

Advice...pull the code first. While a CPS sounds logical to cause shutdown when warm; followed bya normal restart after it cools down, it normally does not produce codes......

Can someone post the steps and procedures to change the CPS?
I still don't know how to pull the code for my car. 1997. S500. 144K.

To pull codes you use a scanner. A simple OBDII scanner will read it if its an engine code.

The CPS is on top of the trans bell housing. Look down from drivers side between the rear of the engine and the firewall. Might need a flashilight to see it. Usually held on with a torx head bolt.

I just today purchased car and when I got home I got same problem as in the first post , and feel little bit scared because don't know what's wrong and how much it can cost to fix ...

Tell us a little bit about the exact problem you have

My problem is exactly same as yours ayayikes . After driving around 30 miles home fuel signal signal starts flashing and check engine light now is on . Car run great just that check engine light is killing . I see your car is same year as mien and have exactly same problem .

Don't be scared.....lol....It wasn't anything wrong wth the engine. U may change your gas cap. it cost less than ten dollars and always keep the gas level over 1/4.
When it happened to me , I get it checked and they said it was a gas leak from the cap, the plastic around is dry (old). Go ahead and get a new one. U will drive the car for couple of days and the Chenck Eng Light will go off.

I also get check engine light when gas is low, but the code I get is P0110 which has to do with the air intake sensor in the MAF. Do you think it is the fuel cap? If so, why would it throw the P0110 code?