Ok so im driving normal when all of the sudden i get a low tire cell on my 08 MCS. Is the rear driver side tire, i pull over and check the pressure and it was 30 psi so i go to the local gas station and fill it up to 38 psi the cel goes away, i drive 25 miles and again the cel comes back on again i check it and it was 34psi, i check for a nail and nothing, i fill it back up this time to 40 psi and the cel still on even after re-starting the car and driving it home.

 

Do you have runflats or not? Either way, sounds like you have a not so slow leak.

 

might want to take it to a tire shop and let them dunk it in water to see if bubbles form.

I did it, and they did not charge me for the service.

 

Also of note is that the system will show a fault if the pressure from side to side is grater than a couple of pounds.

So lets say the passenger rear side was at 37 PSI and you raised the pressure in the drivers rear to 40 then you would still get a fault because they are not close enough in pressure.

Also you should always check all the tires and after adjusting them do a TPMS reset to insure that the system is working on the correctly adjusted pressures.

Air temps changes of 30 degrees will cause the system to possibly show a fault. I.E. if the tires are filled at say an out side temp of 50 degrees and then the temp drops to 15 degrees the next day you can easily have a TPMS light show up. This is a known issue with many TMPS systems as the pressure in the tire varies due to the temperature.

 

Did you reset the TPMS system after filling the tires? Any time you add air, rotate the tires, etc, you will need to reset the system.

 

Two reasons my car has done that...

1.) Got new tires put on and the shop messed up the TPMS sensor, and there was a slow leak through the valve.

2.) Really cold outside temps. Thinner air makes the TPMS read low air pressure, so it sets off the CEL.

 

I didnt know about reseting the system i will try it and let you all know.

 

Set all the tire pressures evenly first, then reset the system.

 

How can i tell if my tires are Runflat? i reset the TPMS and it still telling me is low.

 

Well i followed the instructions from everyone here and finally the "low tire" light is gone...... thank you !!!!!!