Stability control

My girlfriend has a 2000 Bonneville SSEi that the stability control system says service from time to time. The service stability control warning comes on just after the ABS kicks in for no reason when slowing, this is not hard stopping but just normal easy driving, or just anytime. Also once and a while the steering gets a bit hard and then the warning flashs on and stays on. I am wondering if this is a major problem cause when hooked to a scan tool (not one you can buy at Walmart a good GM one) there is no indication of a problem or error code. Could anyone please help?! Thanks!!

I take it that no one has ever had this problem or knows anything about it? It is getting worst and still no help from dealer. I need help!