2003 Chevy Impala

I have taken my car to the dealer cause when I turn the key on in the ignition the car start and the ligth for ABS in TRACTION CONTROL SYSTEM come on and stay on the whole time I m driving. But sometimes when I start the car on the light for those problems don't come on. NOw the dealer did a tune up and says they need to the replace the EBCM and BPMV. What I looking is for a little hope a second opinion. Why is doing that sometimes and not all the time? Can be another problem with the ignition switch? THANK YOU for all the help I love my Impala the engine is great.