From Pennlive.com -
This is indeed a setback for personal privacy rights in Pennsylvania, as the requirement of a warrant issued by a neutral Judge was at least some check on the power of the Police.The Supreme Court's ruling stems from a legal battle over a January 2010 traffic stop in Philadelphia.Two police officers pulled over a sport-utility vehicle driven by Shiem Gary because they believed its window tinting was too dark. The officers then claimed they smelled marijuana coming from the SUV and that Gary told them there was "weed" in the vehicle.Police said a drug-sniffing dog hit on the SUV and a subsequent warrantless search discovered about 2 pounds of marijuana hidden under the hood.Gary challenged whether the police had legally obtained the drug evidence. The case came to the Supreme Court on appeal after the state Superior Court backed Gary. http://www.pennlive.com/midstate/index.ssf/2014/04/divided_pa_supreme_court_oks_w.html
It is likely that Police will still ask drivers for consent to search their vehicles, even when they believe they possess probable cause. This will be done so that if it is later determined the Officer acted on less than probable cause it is irrelevant if the search is consensual. A driver who refuses the search will likely have his or her car searched anyway. But by refusing the driver still retains the ability to challenge the evidence at a later Court hearing.