not exactly sure how or what this button does. was on when i bought the truck i pushed it and now it flashes every time i try to turn it back on. any help is appreciated.

 

You have a 2500, right?

I believe that works with the Tire Pressure monitor system so that you can run lower tire pressure with a light (or no) load and not get a pressure warning. Should be in your owner's manual.

 

that is so you can run lower pressure in your "rear" tires. 45 PSI for light load in my 2500 4x4

 

There is a procedure to engage that so you don't get the TPMS warning light with pressures under the heavy load setpoints. There is a sticker on the door sill with the pressures. I have gotten away with 48 psi in the rears to engage the light load.