Texas DWI Defenses: How DWI Cases Are Won

A DWI charge is not a conviction

Most DWI prosecutions rest on evidence that looks solid but rarely is: an officer’s opinion, a roadside test, and a machine reading. Each can be questioned, and a defense lawyer’s job is to find where the case is weakest. The best defense is not a single magic argument. It is a methodical review of every step, looking for the errors that create reasonable doubt.

The DWI defense framework

Every strong defense follows a framework, working through the case in order: the stop (did the officer have reasonable suspicion?), the arrest (was there probable cause, or did the officer jump ahead?), the field sobriety tests (were they given and scored correctly?), and the science (are the breath or blood results reliable, and do they reflect your BAC at the time of driving?). Finding a single failure in this chain can change the outcome. See the DWI defense framework.

Motion to suppress

A motion to suppress asks the court to throw out evidence that police obtained illegally, such as an unlawful stop, an arrest without probable cause, or a blood draw without a valid warrant. It is brought under Article 38.23, and because Texas has no broad good-faith exception, evidence from an illegal stop or search is excluded even when the officer believed they were acting properly. If the judge grants it, the state can lose the evidence its whole case depends on. See the motion to suppress and the blood search warrant.

Challenging the breath test

Breath results from the Intoxilyzer 9000 are not automatically accurate. They can be challenged on the machine’s calibration and maintenance, operator error, the required 15-minute observation period, mouth alcohol from reflux or a burp, and the assumed 2,100:1 breath-to-blood ratio, which in real people ranges from about 1,100:1 to 3,400:1 and can push someone below 0.08 over the line. Conditions like GERD and diabetic ketoacidosis can inflate the reading. See challenging the breath test.

Challenging the blood test

Blood evidence has its own long list of weaknesses, from the draw to the lab. Defenses include an alcohol swab or unqualified draw, the wrong tube or too little preservative, improper storage that lets in vitro fermentation create alcohol in the tube, coelution that overcounts alcohol in the analysis, and gaps in the chain of custody. Hospital blood tested on serum can also read higher than whole blood. See challenging the blood test.

The science has to pass a reliability test first (the Kelly standard)

Breath and blood results are scientific evidence, and in Texas scientific evidence is not automatically admissible. Under Kelly v. State and Rule 702, the State must prove, by clear and convincing evidence, that the science is reliable on three points: the underlying theory is valid, the technique is valid, and it was properly applied in your case. That last point is where many DWI cases turn. If the State cannot establish reliability, the result can be excluded before the jury ever hears it. The defense has to request that hearing; it does not happen on its own.

Medical conditions and other explanations

Many innocent factors can mimic intoxication or skew a test. Conditions like GERD, diabetes, fatigue, anxiety, and certain injuries can produce signs an officer reads as impairment, affect a breath or blood result, or cause the eye movements officers look for in the HGN test. The rising blood alcohol issue can also mean your BAC was below the limit while you were actually driving. See the medical conditions defense.

Why the right lawyer matters

DWI defense is technical. Challenging breath and blood evidence at the level of the chemistry takes training most lawyers do not have. Deandra Grant Law is led by an ACS-CHAL Forensic Lawyer-Scientist with a Master’s Degree in Pharmaceutical Science and a Graduate Certificate in Forensic Toxicology, who was trained to operate and maintain the Intoxilyzer, teaches gas chromatography at Axion Labs, authors the Texas DWI Manual, and is a certified SFST instructor. Partner Douglas E. Huff holds the same ACS-CHAL designation. With more than 30 years and 500 trials behind the firm, these challenges are made at the level of the science.

Frequently Asked Questions

Can a DWI be dismissed in Texas?

Yes. DWIs are dismissed or reduced when the stop was unlawful, the testing was flawed, or the state cannot prove intoxication beyond a reasonable doubt.

How do you beat a DWI in Texas?

By attacking each part of the state’s case in order: the stop, the arrest, the field tests, and the breath or blood science.

What is a motion to suppress?

A request to throw out evidence police obtained illegally. If granted, it can remove key proof and collapse the case.

Can I challenge a breath or blood test result?

Yes. Both can be challenged on procedure, equipment, the science, and human error.

Can a medical condition cause a false DWI?

Yes. GERD, diabetes, fatigue, and certain injuries can mimic intoxication or skew test results.

Should I just plead guilty to a DWI?

A guilty plea should be a last resort. Many cases have defenses that are not obvious until a lawyer reviews the evidence.

Can the breath or blood evidence be kept out of court?

Sometimes. Texas treats it as scientific evidence under the Kelly standard, so the State must prove it is reliable, including that it was properly applied in your case, before a jury can hear it.

Think You Have No Defense? You May Be Wrong.

Most DWI cases have weaknesses that are not obvious at first. Get a free, confidential review of the evidence with a forensic-trained Texas DWI lawyer. Deandra Grant Law serves Dallas, Fort Worth, North Texas, and Waco. Call (214) 225-7117.

Explore DWI Defense Topics

• The DWI Defense Framework — How a strong defense works through the stop, arrest, tests, and science.
• Motion to Suppress — How illegally obtained evidence gets thrown out.
• Challenging the Breath Test — Calibration, observation, mouth alcohol, and more.
• Challenging the Blood Test — Collection, storage, chain of custody, and lab error.
• Medical Conditions Defense — The conditions that mimic intoxication or skew results.