Over the last 20 years that I have been prosecuting and now defending DUI cases, friends and clients have inevitably asked me if they should blow (or otherwise submit to chemical testing for blood alcohol content) if pulled over for a possible DUI. My answer has always been, "It depends on a number of factors and considerations".
In Illinois, if you refuse to blow or otherwise submit to chemical testing, your DL will, absent any motions to stop it, be suspended for 1 year (called a Summary Suspension or SS). If you do blow etc., and your blood alcohol content (BAC) is .08 or higher, your DL will, again absent any motions to stop it, be suspended for 6 months. So there is a built in incentive to blow. So should you? I tell people what I would do.
If I am SURE that I honestly only had 2-3 beers (or drinks) over the last 3 hours and felt fine I would definitely blow. If I wasn't sure or I really had a lot more to drink, I would probably not blow. That being said, there are factors that can help your attorney to rescind or cancel the Statutory Summary Suspension if you follow the advise below regardless if you blow or not.
Although there are several legal reasons for cancelling an SS, the one used most is that the officer did not have reasonable grounds or probable cause to believe that you were driving a motor vehicle while under the influence of alcohol at the time they arrested you. How does an officer obtain reasonable grounds or probable cause to believe that you were driving a motor vehicle while under the influence of alcohol? When initially pulled over for DUI (or any traffic violation) it is natural for persons to want to cooperate and answer officers' questions. This is commendable from a moral standpoint, but makes our jobs as defense attorneys more difficult. Remember, the purpose of an officer for asking you questions like "Have you had anything to drink tonight" or "how many drinks have you had" is to build a case against you for DUI. DO NOT HELP HIM (or HER)! In this country, you have an absolute right to remain silent and/or not to incriminate yourself. Also remember - DO NOT LIE. If an officer asks you incriminating questions, your answer might be "I don't want to answer that question without an attorney present" or simply "I don't want to answer that question".
At that point the officer is probably going to ask you to exit your car and perform some tests. Again, these tests are designed to build a case against you for DUI. DO NOT AGREE TO DO THEM. You do have an obligation to follow an officer's commands (like get out of the car), but you do NOT have to perform any tests at the scene.
If you are placed under arrest and taken to the police station, you will then probably be asked to blow or submit blood and/or urine to determine your blood alcohol content.
If you have heeded the above advise and there are no obvious signs of intoxication (e.g. you were involved in an accident, you were "all over the road", you slurred your speech or stumbled getting out of or standing outside the car, etc), then there is a good (or at least better) chance that a judge will find that the officer lacked reasonable grounds or probable cause to arrest you at the scene and may then rescind or cancel your SS and may even bar admission of the blow results (if you do blow) at trial. Needless to say, this makes it extremely dificult for the State to prove a DUI case against you.
So remember, to blow or not to blow may not be the most important question, rather what should I do (or not do) leading up to that point.