Challenging a DWI Breath Test in Minnesota

How Minnesota's Breath Test Works

Minnesota's evidentiary breath testing is done on the DataMaster DMT (which replaced the older Intoxilyzer 5000EN). It uses infrared technology to measure alcohol in a breath sample and includes a fuel cell. The machine runs a control (simulator) sample to check accuracy around the time of your test; Minnesota has moved toward a dry-gas standard for this. The test requires two breath samples, and the machine compares them.

The Law Presumes the Test Reliable — But That's Rebuttable

Under Minnesota law (Minn. Stat. § 634.16), breath-test results from an approved instrument, run by a trained operator, are admissible without the state first proving the machine is scientifically reliable. Once the state makes a basic showing — a certified operator and diagnostic checks indicating the device was working — the burden shifts to the driver to show why the result shouldn't be trusted.

What this means for you: The number isn't automatically the last word, but challenging it takes specific, well-supported evidence — not just generalized doubts. That's where an experienced defense, and often an expert, matters.

A Major Current Issue: Machine Maintenance and Calibration Errors

Breath-test results are only as reliable as the machine's maintenance and calibration. This has become a significant, current issue in Minnesota: problems with how the state's breath-test machines were maintained have led to serious questions about the accuracy of many results, and to scrutiny of whether proper protocols were followed. When maintenance or calibration protocols aren't followed, it can create reasonable doubt about a result — and support a motion to suppress or exclude the breath test.

Because this area is actively developing, anyone facing a breath-test DWI should have the maintenance and calibration records for the specific machine closely examined. (See our DWI discovery page for the records to demand.)

The Observation Period

Before a breath test, the officer is trained to continuously observe the subject for a set period (generally about 15 minutes) to ensure they don't belch, regurgitate, eat, drink, or do anything that could introduce mouth alcohol and skew the result. Problems here are a classic challenge:

• If the observation wasn't truly continuous, the result's reliability can be questioned.
• Exactly who bears the burden regarding a proper observation period is an actively contested question in Minnesota courts — making this a live and evolving area.

Mouth Alcohol and Contamination

A breath test is meant to measure deep-lung air, not alcohol lingering in the mouth. Mouth alcohol from belching, regurgitation, acid reflux/GERD, dental work, or recent ingestion can produce a falsely high reading. This is precisely why the observation period exists — and why a flawed observation period and a mouth-alcohol defense often go together.

The Two-Sample "0.02 Agreement" Rule

The machine takes two breath samples, and they must agree within a set tolerance — the two results can't differ by more than 0.02. If they do, the test is reported as deficient. The handling of deficient samples, and what a deficient result means, has been the subject of significant litigation, and a deficient or non-agreeing result is an area to scrutinize.

Other Recognized Challenges

• Margin of error: Every measurement has a margin of error, which can matter enormously when a reading is close to a legal threshold (0.08, or 0.16 for the aggravating factor).
• Radio frequency interference (RFI): Signals from nearby devices have been raised as a potential source of error.
• Body temperature: An elevated body temperature can affect the breath-alcohol reading.
• Partition ratio: Breath testing relies on an assumed breath-to-blood ratio that doesn't hold identically for everyone.
• Machine malfunction / error messages: The machine's own error messages and malfunction history can undercut a result.
• Source code / software: The software controlling the machine has been a long-running reliability battleground; challenging it generally requires a threshold showing of how a defect could affect the result (see our DWI discovery page).
• Operator error: Deviations from training and proper procedure can undermine the test.

A Note on Expert Testimony

Minnesota courts have limited a defendant's expert testimony to causes of error supported by evidence in the specific case — an expert generally can't testify about hypothetical, generalized causes of false readings without record support. So the strongest breath-test challenges tie a recognized source of error to the concrete facts and records of your test.

Breath, Blood, and Urine Are Governed Differently

Remember that the rules differ by test type: refusing a breath test is a crime, while blood and urine tests generally require a warrant. For those distinctions and for challenges specific to blood and urine, see our pages on DWI chemical testing and challenging blood and urine tests.

Key Terms

• DataMaster DMT: Minnesota's current evidentiary breath-test instrument.
• Section 634.16: The statute making approved breath-test results admissible without antecedent reliability testimony.
• Observation period: The pre-test period of continuous observation to prevent mouth alcohol.
• 0.02 agreement: The required closeness between the two breath samples.
• Mouth alcohol: Alcohol lingering in the mouth that can falsely raise a result.