The Fourth Amendment has two clauses, the second of which states that no warrant shall be issued except upon probable cause. The exact meaning of "probable cause" is not clear and comes from judicial interpretations. The following is the most commonly used definition of probable cause
As applied to drunk driving cases, this means that a police officer who stops a vehicle must believe that the driver of the vehicle is driving under the influence before the officer can stop the car and test the driver. The police officer operates entirely on the information he/she observes. No hunches or inferences are allowed here.
A DUI case has 3 stages:
Stage 1: the vehicle is stopped.
Stage 2: the driver is detained.
Stage 3: the driver is arrested.
Here’s where probable cause becomes key. If there was no probable cause to stop the vehicle, all evidence obtained afterwards must be suppressed. Prosecution cannot use it in court.

In DUI cases, this usually reduces the evidence to only the driver’s voluntary statements or the officer’s observations. Under these circumstances, the case is commonly dismissed.
In my professional opinion, probable cause to stop the driver is almost always subject to attack. The matter is litigated in court through Motions to Suppress. It’s a powerful tool for the lawyer who knows how to use it. You’ll find precisely that kind of lawyer when you call DUI Terminator, Kenton Koszdin at 800-Kick DUI. Call now. You’ll be glad you did.