How Can You Challenge Breathalyzer Results in an Illinois DUI Case?

 Posted on October 22, 2025 in DUI/DWI

If you blew over the legal limit during a DUI stop, you still have a chance to fight the charges. Breathalyzer results are not always accurate or reliable. There are actually several legal and scientific ways to challenge those numbers in court. The first step is to talk to an experienced Cook County, IL DUI defense lawyer if you believe your test results were wrong.

Can You Refuse a Breathalyzer Test in Illinois?

Illinois has an implied consent law under 625 ILCS 5/11-501.1. By driving on Illinois roads, you automatically give your consent to undergo chemical testing during a DUI stop. Of course, the officer also has to have probable cause for an arrest.

You can refuse a breathalyzer, but there are consequences. A first refusal leads to a one-year driver’s license suspension. Repeat refusals can mean a three-year suspension. Even if you refuse, the officer may still arrest you and use other evidence, such as field sobriety tests or dashcam footage, in court.

Are Breathalyzer Tests Accurate?

Breathalyzers measure the alcohol concentration in your breath, not directly in your blood. The reading is then converted into an estimated blood alcohol concentration (BAC). According to the DUI statute, you can be charged with DUI if your BAC is 0.08 percent or higher. However, these machines can produce false readings under several circumstances. 

What Are the Most Common Problems With Breathalyzer Tests?

The first thing an attorney will do in a failed breath test case is look for issues with the test and how it was administered. Some of the most common problems to look for include:

• The officer did not follow the 20-minute observation rule required by Illinois Administrative Code §1286.310.

• The breathalyzer machine was not properly calibrated or certified.

• The officer lacked the correct certification to operate the device.

• Medical conditions, such as GERD or diabetes, affected the results.

• Mouthwash, breath spray, or dental work caused residual alcohol readings.

• There was a delay between driving and testing, allowing your BAC to rise after you stopped driving.

• Poor record-keeping or missing maintenance logs could impact the validity of the reading.

Can a DUI Be Dismissed if the Breathalyzer Was Wrong?

A DUI case can sometimes be dismissed if the breathalyzer results are proven unreliable. When the evidence does not meet Illinois’ legal standards, the prosecution’s case may fall apart. If the breath test was improperly handled, the machine malfunctioned, or the officer did not follow required testing procedures, a judge can decide to exclude the results. Once that happens, the state may not have enough proof to move forward with the charge. Every case is different, but an experienced defense attorney can review the details and determine whether the breathalyzer results can be challenged or thrown out.

Schedule a Free Consultation With a Chicago, IL DUI Defense Attorney

Challenging breathalyzer evidence requires a careful, intentional investigation. A knowledgeable Cook County, IL DUI defense lawyer knows where to look for holes in the prosecution’s case. At Law Offices of James F. DiQuattro, our accomplished and dedicated attorney fights aggressively for every client. He will stand by your side and ensure no one violates your rights.

Call 312-627-9482 today to schedule your free consultation and start building your defense.