Driving under the influence (“DUI”) is a crime in California. Most (if not all) states have their own DUI laws, and California is no exception with Vehicle Code Section 23152 (“VC 23152”). In this section we will discuss the particulars of California’s DUI laws and possible defenses to charges arising there.


The prosecution’s case in a DUI usually boils down to two sections of proof: evidence that you were, in fact, driving a vehicle and evidence that you had some version of alcohol, drugs, or a combination of both in your system at the time. The prosecution has to prove, beyond a reasonable doubt, that

  • The defendant was operating a vehicle AND

  • At least one of the following

    • The defendant was “under the influence” of alcohol at the time they were driving

    • The defendant had a BAC of at least 0.08%

    • If driving a commercial vehicle or a “ride for hire” vehicle, the defendant had at least 0.04% BAC

    • The defendant was under the influence of any drug OR

    • The defendant was under the combined influence of any drug and alcohol

Notice that a DUI case does not always require the prosecution to prove that the defendant was “under the influence” of alcohol or was incapable of driving safely. If a jury feels, beyond a reasonable doubt, that the defendant was driving a car with a BAC over 0.08%, for example, then they will find that defendant “guilty” of DUI even if they also feel that the defendant was capable of driving safely. Similarly, in cases where the prosecution alleges that the defendant was merely “driving under the influence” of alcohol or drugs, they can prove circumstantially that the defendant had drugs or alcohol in their system such that it impacted their driving. For that type of DUI charge, the prosecution need not show that the BAC was over a certain limit, although evidence of the defendant’s high BAC would probably help convince a jury to find the defendant guilty.

If, however, the jury had reasonable doubt that the defendant was driving, or that the defendant’s BAC was above a certain level or whether the defendant was “under the influence, they would find the defendant “not guilty” of DUI.



While it seems obvious, remember that the prosecution has to prove that the defendant was driving a vehicle, AND that, while driving, the defendant was “under the influence” of drugs or alcohol or had a BAC above a certain limit. Where the prosecution cannot show that the defendant was ever driving, or that the defendant was driving with too much alcohol in their system, then their case might be weaker.

In some DUI cases the defendant is arrested on suspicion for DUI during a vehicular traffic stop. In those case, the prosecution might have an easier time proving that the defendant was, in fact, driving the car during a relevant time period. However, consider also a case where a defendant drives their car into town sober, parks their car, walks to a bar, drinks all night, and returns to their car. The defendant never starts the car or moves it, but instead just sits inside the car and sleeps. If the defendant was arrested and charged with DUI, he would probably be found “not guilty” because, while he did drive his car at some point, he did not do so while drunk or with a high BAC.


In some DUI cases there are no test results available and the prosecution’s case rests largely on circumstantial proof that the defendant was intoxicated or under the influence of drugs or alcohol. To do this, the prosecution might base most of their case on evidence from “field sobriety tests”, if any were done. Examples of this include the “one leg stand” and “walk and turn” that police officers have DUI suspects perform before arresting them for DUI. Field sobriety tests are not always reliable indicators of intoxication, however. A well-prepared defense of a DUI case should look into whether police exaggerate or overstate the defendant’s “failures” on field sobriety tests, and whether other factors like the weather, the terrain, or the defendant’s physical disabilities made it seem that they might be “failing” certain tests when in fact they were perfectly sober.


In many DUI cases, however, there is chemical testing available in the form of breath or blood samples. In those cases, if the test results show that the defendant’s BAC was above the allowable amount, and the jury accepts those test results as true, then it does not matter that the defense proves that the defendant was not actually “too drunk to drive”, because driving with a BAC that is too high is “per se” DUI.

It becomes important in these cases for the defense to explore whether the testing was done properly. In a breath case, was the breath machine properly maintained and calibrated? If not, then any incriminating results might not be reliable. In blood cases, was the sample properly preserved before being sent to a lab for testing? Was it even the right person’s blood that got tested? Could any other chemicals have interfered with testing for the presence of alcohol? These questions are worth exploring in any well-prepared DUI defense where a blood sample is involved.

One point is worth clarifying: there is a difference between the “roadside” preliminary alcohol screening test and the chemical tests done after the defendant was arrested. The preliminary test (or “PAS” for short) is usually only admissible to show that an officer has “probable cause” to arrest the defendant for DUI and then prompt the defendant to give a more reliable chemical test while in custody. The PAS test is always based on a breath sample. A “chemical test”, however, is usually taken after the defendant has already been arrested on suspicion of DUI. The results of this test are usually what a DUI prosecution is likely to base their case on.


While not necessarily a “defense” to a charge of DUI, a good DUI defense attorney should always explore the possibility of a “motion to suppress” any evidence taken in their client’s case. Where police obtain evidence against a defendant through unlawful means, the court might be inclined to “suppress” or “keep out” that evidence at trial, forbidding the prosecution from using it against the defendant. This is true in all criminal cases. In DUI cases, however, a successful motion to suppress might be fatal to the prosecution’s case.

Police cannot stop or detain someone without “reasonable suspicion”, which means articulable facts to support a reasonable conclusion that criminal activity (like a traffic violation, or, of course, DUI, is afoot) is afoot. Police cannot arrest someone for DUI and prompt them to take a chemical test without “probable cause” to believe that the defendant is committing DUI, which means that the police must detect “objective signs of intoxication”, such as slurred speech, the odor of alcohol, and poor performance on sobriety tests.

Consider, for example, a case where police stop the defendant while he is driving, and during the stop, the police detect an odor of alcohol and notice that the defendant is slurring his speech. The defendant then agrees to do field sobriety tests which he does poorly on, so he is arrested and his chemical tests place his BAC above 0.08. In that case, the prosecution probably has more than one way to show that the defendant was “DUI”, as the observations of his behavior and field test performances, combined with his test results, are all consistent with alcohol intoxication. However, assume now that at a motion to suppress, the judge determines that the police had no lawful reason to stop the defendant’s car in the first place. Then, the judge might decide to “suppress” the chemical tests and the officer’s observations of the defendant’s behavior because they all stem from the illegal stop.


DUIs in California are treated more seriously depending how many “prior” DUIs the defendant has on their record. A first DUI can be punished for 96 or 48 hours, up to six months in prison, and penalties increase for additional DUI convictions within the same 10 year period. The second DUI in this period can be punished for 90 days or 96 hours up to 12 months, a third for twelve months as well but with a high mandatory penalty of 120 days. A fourth DUI is chargeable as a felony, and can be punished by 16, 24 or 36 months in prison, or 6-12 months of jail.

The DMV also imposes its own penalties for DUIs, as well. A DUI conviction will often lead to a license suspension for a certain period of time, and the DMV can also require the defendant to install an ignition interlock device on their car at the defendant’s expense. People convicted of DUI are also required to attend DUI offender programs of various lengths, as well. And fines and penalty assessments usually total at just over $2000. When facing a DUI charge in California, be sure to discuss all of the possible consequences of a conviction with your attorney.