1999 ML430 keeps going into limp mode
 

My 1999 ML 430 keeps going into limp mode. Truck will driver fine for couple minutes with no brake light on, then brake light will come on and beeps like the handbrake is left on.
I checked handbrake and switch and its not on , fluid is good and pads are fine.
What else can i check?

The parking brake indicator and audible beep are telling you that the traction system is off-line. You'll need to have the codes read out.