How to Fight a California DUI: A Charge Is Not a Conviction

Reviewed by Ron Chini, Esq. · CA State Bar No. 263308 · DUI defense attorney in Irvine, CA since 2009.
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If you were arrested for driving under the influence in California, you have not been convicted of anything. An arrest is an accusation, not a verdict. To win a conviction, the prosecutor must prove every element beyond a reasonable doubt: that the stop was lawful, that the testing was done correctly, and that your blood alcohol concentration was actually over the limit while you were driving. If any one link in that chain is weak, the whole case can weaken with it. The defenses below are the ones that come up most often in real California DUI cases. Which of them apply to you depends entirely on the facts of your arrest, which is why a careful review with attorney Ron Chini matters.

The Prosecution Has to Prove Every Link

A California DUI case is usually built on a sequence: the reason for the stop, what the officer observed, the field sobriety tests, and the chemical (breath or blood) test result. Under Vehicle Code 23152 (DRAFT — verify), the state can charge you under subsection (a) for driving while impaired, and separately under subsection (b) for driving with a blood alcohol concentration (BAC) of 0.08% or higher. The 0.08% limit generally applies to most adult drivers; the threshold is typically lower for commercial drivers (around 0.04%) and for drivers under 21 (as low as 0.01%) (DRAFT — verify thresholds).

Each step in that sequence has rules behind it, and each one is a place where the case can be challenged. A good defense rarely depends on a single dramatic moment. More often it comes from showing that the evidence is not as solid as the report makes it sound. Remember too that the BAC the state cares about is your level at the time of driving, not necessarily the number that printed out at the station an hour or more later.

Was There a Lawful Reason for the Stop? (Fourth Amendment)

Before an officer can pull you over, the Fourth Amendment requires reasonable suspicion that a law was being broken, such as a traffic violation or signs of unsafe driving. An officer cannot stop you on a hunch. If the stop itself was unlawful, your attorney can ask the court to suppress the evidence that came after it, under what is sometimes called the "fruit of the poisonous tree" doctrine.

The same principle applies to blood draws. Generally, police need either your valid consent or a warrant to take a blood sample. A blood draw taken without consent and without a warrant may be challengeable, and if that evidence is suppressed, the case can fall apart. When a stop or a search crosses the line, the consequences can reach all the way to the chemical test result.

Breath Test Problems: Rising BAC, Mouth Alcohol, and Title 17

Breath machines are not infallible. Three common attacks come up repeatedly in California cases:

• Rising BAC. Alcohol keeps absorbing into your blood for roughly 30 to 90 minutes after your last drink (DRAFT — verify range). If you drank shortly before driving, your BAC may have still been climbing. That means your level at the moment of the stop could have been under the limit even though a test taken later read higher. California's so-called three-hour presumption (that a test within three hours reflects your driving-time BAC) is a rebuttable presumption (DRAFT — verify), and rising-BAC evidence is one way to rebut it.
• Mouth alcohol, GERD, and acid reflux. A breath machine is supposed to measure deep-lung air. If alcohol lingers in your mouth, or if a medical condition like GERD, acid reflux, or a recent burp sends a small amount of alcohol back up from the stomach, the machine can read artificially high. This is why Title 17 of the California Code of Regulations generally requires a continuous observation period (commonly cited as 15 minutes) before the test (DRAFT — verify duration). If the officer did not watch you closely the whole time, or missed a belch or regurgitation, that reading is open to challenge.
• Title 17 and calibration violations. California regulations set strict rules for how breath tests must be administered, how often the machine must be calibrated and maintained, and that the operator must be properly trained. Missing calibration logs, maintenance gaps, or a deviation from procedure can be grounds to challenge, or even exclude, the result.

Blood Sample Handling and Field Sobriety Tests

Blood tests carry their own vulnerabilities. A sample must be drawn, stored, and transported correctly. Problems with chain of custody, improper preservation, or contamination can call a blood result into question. Your attorney can request the records behind the number to see whether the sample was handled the way the rules require.

Field sobriety tests (FSTs) are far less reliable than they look. Even the three standardized tests endorsed by NHTSA, the horizontal gaze nystagmus, the walk-and-turn, and the one-leg stand, have published accuracy rates well short of certainty (commonly cited around 77%, 68%, and 65% respectively) (DRAFT — verify figures), and only when administered under ideal conditions. Roadside conditions are rarely ideal. Uneven pavement, poor lighting, cold weather, nerves, fatigue, footwear, age, weight, and medical or diet conditions can all make a sober person look impaired. In California, these tests are generally voluntary, and a poor performance is evidence that can be explained, not proof of guilt.

Which Defense Applies to You?

There is no one-size-fits-all DUI defense. The right strategy depends on the specific facts: why you were stopped, what you said and did, what tests were run, your medical history and what you had eaten or drunk, and whether the officer followed every required procedure. Sometimes the strongest move is challenging the evidence in criminal court; sometimes it is the parallel DMV hearing over your license, which runs on its own short deadline. The only way to know which doors are open in your case is to have someone go through the police report and the testing records line by line.

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Ron Chini, Esq.

DUI Defense Attorney · CA State Bar No. 263308

Ron has focused on DUI and criminal defense from his Irvine office since 2009. You work directly with him — not a paralegal or a call center.

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