Could My Positive Breathalyzer for an Illinois DUI Test Be Wrong

 Posted on June 30, 2025 in Criminal Defense

If you recently blew above the legal limit during a DUI stop, you are likely concerned about how it will impact your case. Most people assume breathalyzer machines are correct, but in reality, these devices are highly sensitive. Their readings can be affected by everything from calibration errors to medical conditions. If you are facing charges based on a questionable blood alcohol concentration (BAC) result, a Naperville DUI defense lawyer can help you understand your legal options and how to challenge the evidence effectively.

Understanding the Laws that Govern DUI Cases in Illinois

DUI cases in Illinois are primarily governed by 625 ILCS 5/11-501. Under this statute, it is illegal to drive a vehicle with a BAC of 0.08 percent or more, and breathalyzer tests are standard procedure after DUI arrests.

Police officers can ask to take a preliminary BAC screening with a portable breath-measuring device, but before they can use a breathalyzer or other evidential breath test, they have to have probable cause and make an arrest. Police will typically use field sobriety tests or erratic driving patterns to establish probable cause. You can refuse the preliminary screening, but you cannot refuse a breathalyzer or other chemical test once you have been arrested without serious consequences.

Statute 625 ILCS 5/11-501.2 outlines the procedures and standards for administering chemical tests, including breath tests. This law allows test results to be used as evidence in court, but only if specific protocols are followed, such as observing the suspect for 20 minutes before testing and ensuring the machine is properly certified.

Additionally, 625 ILCS 5/2-118.1 says there is an automatic driver’s license suspension triggered by either a failed or refused chemical BAC test. However, you have the right to a hearing to contest the suspension, and an experienced defense attorney can challenge the validity of the breathalyzer at the hearing.

Limitations of Breathalyzer Tests in an Illinois DUI Case

While breathalyzers are common tools in DUI enforcement, several limitations can lead to inaccurate or misleading results:

• Calibration errors: The devices must be calibrated regularly. If maintenance is skipped or improperly logged, results can be invalidated.

• Operator error: Officers must be trained and certified to use these machines. Mistakes in how the test is administered can render results unreliable.

• Residual alcohol: Breathalyzer tests cannot distinguish between alcohol in the bloodstream and alcohol in the mouth. Using mouthwash, burping, or having acid reflux can falsely elevate BAC readings.

• Medical conditions: Conditions like GERD or diabetes can produce substances on the breath that mimic alcohol, leading to false positives.

• Environmental factors: Nearby chemical fumes, such as from paint or cleaning supplies, can interfere with the sensors on a breathalyzer.

Each of these variables can be used to cast doubt on the accuracy of your result, and if appropriate, your attorney can help you build a defense based on evidence of a faulty breath test.

Call for a Free Consultation With a Naperville, IL DUI Defense Attorney

You do not have to blindly accept a breathalyzer result at face value, and you should not. The device could have been faulty, or the test may have been mishandled. Even your medical conditions could play a role in your defense. With the right strategy, you may be able to avoid conviction, reduce penalties, or protect your driving privileges. Call 630-416-7600 to schedule your free consultation with an Illinois DUI defense lawyer at the Law Office of Philip R. Nathe today.