why beacuse they are fn junk . i have one it starts from one sensor to another i have gone from cadillac to gmc to chev dealers all have the same song and dance cause with out the computer they cant fix it mechanics my ass they are part changers , my father is old school mechanic. plus gm thought they were smart making a shell and selling it with different names but are have the same diseases, they are terrible and i will never find why my escalade light goes on and why i have problem turning right i replaced the pump, stering assembly all gm junk made by companys over seas to the lowest bidder that gets to keep the tech specs an knows how not to make it so theirs will be better