Top 10 Legal Defenses For Fighting a California DUI Charge

The top 10 legal defenses to California driving while intoxicated ("DUI") charges fall into three categories:

  1. you weren't actually intoxicated,1
  2. your driving wasn't actually impaired2, and/or
  3. the officer who arrested you for DUI didn't follow proper procedures.

As an experienced California DUI defense attorney can tell you, a DUI arrest does not have to mean a DUI conviction. You can avoid life-changing California DUI penalties3--including hefty fines and a driver's license suspension--by fighting DUI charges with a strong defense strategy.

The top 10 legal defenses to California DUI charges are:

1. Top DUI Defense #1: Bad Driving Does Not Automatically Equal DUI

You can fight DUI charges by arguing that you were merely driving erratically or poorly--but NOT driving under the influence. This top California DUI defense is especially helpful with charges that you were "driving under the influence" under Vehicle Code 23152(a) VC.4

One of the first things prosecutors focus on during a California DUI case is your driving pattern. They routinely have the DUI arresting officer testify that you were driving in a manner "consistent with" someone who was under the influence of alcohol or drugs. Often, this so-called "pattern" includes allegations that you were speeding or weaving within your lane.

An experienced DUI lawyer rebuts this evidence by having the officer testify about all of the ways that you drove properly and safely. A DUI attorney will elicit testimony from the arresting officer that:

  1. the majority of traffic violations are actually committed by sober people, and
  2. driving pattern is not a reliable predictor of DUI.

The National Highway Traffic Safety Administration (NHTSA) -- the nation's leading authority on DUI -- says that cues based on driving patterns are predictive of DUI only 35% of the time.5 Even the National District Attorneys Association admits that driving behaviors are sometimes "quite nuanced."6

Example: Tony is driving on the 405 Freeway after having a late-night drink with a friend. He is listening to music on his phone. When he picks up his phone to change the playlist, he drifts into the next lane. Tony is pulled over by a California Highway Patrol (CHP) officer and arrested for DUI.

Tony's DUI defense attorney gets the officer to admit that Tony was driving within the speed limit, pulled over as directed, parked without difficulty, and otherwise was driving with "the caution characteristic of a sober person".7

The attorney also gets the officer to admit that sober people often drift into other lanes for reasons having nothing to do with drug or alcohol consumption--for example, being distracted by their smartphones. This defense to Tony's DUI charges leads to a "not guilty of DUI" verdict.

2. Top DUI Defense #2: Objective Symptoms of Intoxication Are Not the Same Thing as DUI 

Another effective way to fight California DUI charges is to challenge the prosecution's use of physical symptoms of intoxication to argue that you were "under the influence."

Your physical appearance plays a big role in your California DUI investigation. The officer who arrested you for DUI will undoubtedly testify that you were "under the influence" because you had

  • red, watery eyes,
  • slurred speech,
  • a flushed face,
  • the strong odor of alcohol on your breath, and/or
  • an "unsteady gait".

Incidentally, these "objective signs and symptoms of intoxication" are all listed on a pre-printed DUI arrest form called Form 5.2.5. This form is used by the CHP, the Los Angeles Police Department (LAPD), and other local law-enforcement agencies.8 Using Form 5.2.5, an officer can simply "check off" that you displayed these signs / symptoms, without further elaboration.

A skilled DUI lawyer can defend you against DUI charges, including VC 23152(a) charges, by addressing the "innocent" explanations that could have led to those signs. For instance,

  • allergies,
  • a cold,
  • fatigue, and
  • eye irritation.

are all common causes of red eyes.

Glasses of beer
Experienced DUI defense attorneys know that "the smell of alcohol on someone's breath" doesn't necessarily mean they drank alcohol.

A knowledgeable DUI attorney will also elicit testimony that alcohol has no odor What people perceive as alcohol on the breath is actually the smell of other things commonly found in both alcoholic and non-alcoholic beverages -- such as the malt and hops in beer.

Example: Sam is on trial for DUI. Officer Lopez, the arresting officer, testifies at his trial.

Officer Lopez testifies that, when he pulled Sam over, he observed that Sam had red and watery eyes, a flushed face and breath that smelled like beer. But on cross-examination by Sam's Newport Beach DUI defense lawyer, Sheriff Smith admits that he never questioned Sam about other possible causes.

As it turns out, Sam had been playing beach volleyball all day.on the day he was arrested. The sun accounted for his red eyes and flushed face. He had also had a couple of Coronas and several non-alcoholic beers over the course of the day, which explains the odor on his breath--but was not nearly enough alcohol to make him "under the influence" for purposes of California DUI law.

These facts cast strong doubt on the assertion that Sam was under the influence--and prevent the prosecution from getting a guilty verdict in his DUI case.

3. Top DUI Defense #3: Field Sobriety Tests (FSTs) Don't Accurately Measure Impairment

If you are charged with DUI in California, and the prosecution's evidence includes the results of Field Sobriety Tests (FSTs), you and your attorney may be able to challenge those results as part of your DUI defense strategy.

FSTs often are heavily relied on by the DUI "prosecution team" -- the prosecutor, the arresting officer, and the California DUI criminalist. These "experts" almost always testify that you "performed poorly" on these tests. As a result, they conclude that you were guilty of drunk driving.

Officer conducting field sobriety test
The unreliability of field sobriety tests can be part of a California DUI defense strategy.

Your DUI defense lawyer will explain how balance and coordination during FSTs can be affected by:

  • your natural physical coordination,
  • nerves,
  • fatigue,
  • your clothing,
  • flat feet, and
  • a variety of other issues.

Example: Lisa is charged with and on trial for DUI in Los Angeles.

An LAPD officer tells the jury that Lisa performed poorly on her FSTs. But on cross examination, Lisa's DUI lawyer establishes that Lisa took her FSTs on Sunset Boulevard, outside a busy bar with a line of people watching. The night was cold and windy, cars were speeding by, and Lisa was in 3-inch high heels.

Lisa's DUI attorney convinces the jury that any or all of these non-alcohol-related factors could have caused her "poor performance" on the FSTs--and successfully fights the DUI charges with this defense strategy.

Your DUI defense attorney will also challenge the reliability of the FSTs themselves. The NHTSA claims that FSTs accurately predict alcohol impairment 91% of the time.9 But this percentage – even if true – assumes that:

In reality, all of these factors can vary greatly--and make the unreliability of FST results a viable DUI legal defense.

4. Top DUI Defense #4: "Mouth Alcohol" Led to a Falsely High BAC Result

Falsely high BAC results can also be the grounds for a successful legal defense to DUI charges--particularly charges that the defendant drove with a BAC of 0.08 or above under Vehicle Code 23152(b) VC.

Before giving you a California DUI breath test, an officer must continuously observe you for fifteen (15) minutes. This is to make sure that during this time you do not put anything containing alcohol into your mouth, including:

  • drinks,
  • medicines (such as homeopathic medicines or cough syrup), or
  • mouth spray or mouthwash.
So-called mouth alcohol can produce a falsely high BAC breath test result.

The officer must also make sure that you do not belch, burp or regurgitate. Doing any of these things could bring alcohol from your stomach into your mouth--creating the phenomenon known as "residual mouth alcohol," which functions as a common defense to DUI charges.

The accuracy of California DUI breath testing equipment relies on the measurement of "deep lung air." But when you blow into a breath testing device and there is alcohol in the mouth, it mixes with air from the lungs. This can cause your blood alcohol content (BAC) to register falsely high.

Example: Becky has been arrested for DUI. 

She admits to her DUI defense attorney that she drank wine with dinner before her DUI arrest. She also says that the meal was unusually rich, and that she suffers from gastroesophageal reflux disease (GERD). The meal triggered an episode of acid reflux, which cause her to burp repeatedly while the officer was administering her DUI breath test.

Becky's drunk driving defense attorney calls the prosecutor and lets her know that he intends to call a toxicologist to the stand in Becky's trial. The toxicologist will testify that burping can produce "residual mouth alcohol" and artificially inflate BAC test results. When presented with this DUI defense strategy, the prosecutor offers Becky and her attorney a plea bargain to the reduced charge of "dry reckless."

5. Top DUI Defense #5: The Officer Didn't Conduct a Proper 15-Minute Observation Period

We mentioned above that the arresting officer is required to observe you for 15 full minutes before your DUI breath test.10 Questioning whether that observation actually took place is a common DUI defense that our attorneys utilize.

Many officers don't actually "observe" during the observation period. Instead, they do paperwork and/or set up the breath test machine. Showing that the officer failed to properly conduct the observation calls into question not only your breath test results, but the entire DUI investigation.

Example: At Tim's DUI trial for Vehicle Code 23152(b) VC DUI, an officer from the San Bernardino County Sheriff's Department testifies that he "continuously observed" Tim for 15 minutes before his breath test. He says that during that time nothing unusual happened.  

On cross-examination, however, Tim's DUI defense attorney gets the officer to admit that  the 15-minute period took place during the drive to the station. Tim was alone in the backseat during this time. The officer is forced to admit that he couldn't have seen Tim burp, belch, hiccup, or regurgitate--any of which might have inflated Tim's BAC results.

As a result, Tim is able to successfully fight his DUI charges.

6. Top DUI Defense #6: The Officer Didn't Comply With California's Title 17 Regulations on Blood and Breath Testing

Title 17 violations in the administration of DUI blood tests can be used to fight DUI charges.

California Code of Regulations Title 17 governs how DUI blood and breath tests must be conducted. Requirements include:

  • A 15-minute observation period (described above),
  • The proper training of personnel conducting the chemical tests,
  • Proper administration of the tests,
  • Regular calibration and maintenance of the testing equipment, and
  • Proper collection, handling, and storage of blood (or, in rare instances, urine) samples.11

If Title 17 regulations are not strictly observed, your breath test or California DUI blood test results could be tainted. An experienced DUI defense lawyer can use failure to follow even one regulation to call your entire DUI investigation into question and successfully defend against DUI charges.

Example: Rick is on trial for California Vehicle Code 23152(b) VC DUI in Ventura County. 

After the Ventura County District Attorney examines her expert witness -- the DUI criminalist -- the jury hears that Rick's blood test revealed a 0.10% BAC.

But during cross-examination by Rick's DUI defense attorney, the criminalist is forced to admit that the preservative contained in the vial used to collect and store the blood sample had expired, and the arresting officer didn't properly shake or store the sample--two Title 17 violations.

Rick's DUI lawyer is therefore able to convince the jury that these Title 17 violations could have invalidated Rick's 0.10% result and that Rick should be found not guilty of DUI.

7. Top DUI Defense #7: Your BAC Was "On the Rise"

"Rising blood alcohol" is another commonly effective DUI defense.

According to Burbank DUI defense attorney John Murray12

"There is nothing illegal about drinking before driving. What is illegal is being impaired at the time you drive. When you drink, your BAC rises rapidly and steadily until it reaches its maximum level. During this time, your BAC is "on the rise." It takes, on average, about 50 minutes for BAC to reach peak levels -- though depending on various factors it can take as much as two or three hours."

Rising BAC can be a very effective DUI defense.

If you had rising blood alcohol when you were pulled over, the results of your DUI chemical test could be wrong. Your BAC could have risen to over the legal limit during the lengthy period of your DUI investigation. Again, the only thing that matters is what your level was at the time you drove--meaning that you have a strong, valid defense to DUI charges.

Example: Sheila has a couple of quick shots with her friends at a Palm Springs bar. She leaves almost immediately afterward.

Sheila only lives half a mile from the bar. When she is stopped by a local sheriff due to a burned-out taillight, the officer smells the drinks on her breath. He starts a California DUI investigation, which includs field sobriety tests.

By the time Sheila gets to the station and submits to a breath test, her BAC is 0.09%.

But Sheila's DUI defense lawyer should be able to get the prosecutor's expert to admit that Sheila's body probably hadn't fully absorbed the alcohol when she was driving home. This would mean that her BAC was below the legal limit when she drove and that she can successfully fight the driving under the influence charge.

8. Top DUI Defense #8: You Weren't DUI Because You Were Mentally Alert

The difference between physical impairment and mental impairment is the basis of another commonly helpful California DUI defense.

Officers routinely testify that DUI suspects displayed physical signs of impairment. But they don't always testify that defendants showed signs of mental impairment.

If you were only physically but not mentally impaired, your attorney may be able to argue that you were not actually DUI.

DUI toxicologists know that it is highly unusual for someone who is drunk to be physically -- but not mentally -- impaired. A savvy DUI lawyer and expert witness can establish that someone who showed no signs of mental impairment probably had some other explanation for physical signs resembling DUI.

Example: John is pulled over in Long Beach because he is holding his cell phone while driving. He is polite and coherent; he responds to questions appropriately; he follows all the officer's instructions when performing FSTs.

Nevertheless, John exhibits physical signs of impairment, including a lack of balance and shaky hands. So even though his preliminary alcohol screening (PAS) breath test shows a BAC of only .07, John is arrested and charged with DUI.

Fortunately, John's Long Beach DUI defense attorney retains an expert witness in DUI toxicology. The expert testifies that because John was mentally alert, it is highly unlikely that he had driven drunk. John's physical impairment was more likely the result of nerves, fatigue, medication, or something other than alcohol. This testimony helps John beat the DUI charges.

9. Top DUI Defense #9: Hypoglycemia, Diabetes or a High Protein Diet Falsely Inflated Your BAC

Medically savvy DUI defense attorneys know that medical conditions like diabetes and certain popular diets can form the basis of a successful defense to Vehicle Code 23152(a) or 23152(b) DUI charges.

Normally, our bodies get fuel from dietary carbohydrates. Under certain conditions, however, the body has to break down stored fats for fuel. Such conditions include:

  • Fasting,
  • High-protein / low carbohydrate diets (such as Paleo or Atkins), and
  • Diabetes.

During the process of burning fat, the liver produces toxic byproducts called “ketones.” Ketones are chemically similar to the isopropyl alcohol found in solvents such as acetone.

Some of these ketones are excreted in the breath. Unfortunately, California breath testing devices can be tricked by ketones. This is because they don't always reliably distinguish isopropyl alcohol from ethyl alcohol, the type found in alcoholic drinks. This can lead to a falsely high BAC reading on a DUI breath test--and an unfair DUI charge.

Man blowing in breathalyzer
Ketosis can simulate a high BAC on a DUI breath test--and form the basis for a DUI defense.

“Ketosis” can also produce other symptoms that resemble alcohol-based impairment, such as:

  • confusion,
  • lack of coordination, and
  • breath that smells like alcohol.

Example: Leo is stopped at a California DUI sobriety checkpoint in Riverside. An officer notices that Leo's eyes are red and that Leo seems confused. Leo performs poorly on FSTs, and a preliminary breath test shows his BAC at .10%.

After Leo is arrested, he chooses to take a DUI blood test rather than another breath test. The blood test shows Leo's BAC to be just .05%.

It turns out that Leo had been working on a project on his computer for the better part of three days straight. During that time he had eaten almost nothing. When the project was finally finished, he had a beer to celebrate. Because Leo's DUI attorney understands the potential of ketones as a DUI defense, he is able to convince the prosecutor to drop the DUI charges.

10. Top DUI Defense #10: The Arresting Officer(s) Didn't Follow Proper Procedures

Failure of police to follow proper procedures is a powerful defense against California VC 23152 charges--just as it is against charges of many other crimes.

A California drunk driving investigation is supposed to be safeguarded by procedures to protect you from police misconduct. These include:

If any of these protections is violated, your California DUI lawyer will request a "suppression hearing"  -- otherwise known as a "Penal Code 1538.5 hearing." The hearing will serve to:

  • exclude any evidence that wasn't properly obtained, and
  • give your lawyer a "pre-trial" opportunity to illuminate holes in the prosecution's case--and possibly persuade them to drop or reduce DUI charges.

Example: Officer Joe stops Lucy for driving too slowly (Vehicle Code 22400) and for making too wide a turn. A PAS breath test shows that Lucy has a BAC of .06%. Based on the "totality of circumstances," Officer Joe arrests Lucy for DUI under VC 23152(a).

After the arrest, Officer Joe asks Lucy how much she much she had to drink and whether she thought she was drunk when she drove. Only afterward -- when they are at the station -- does he read Lucy her Miranda rights.

Lucy's DUI attorney requests a suppression hearing as part of his strategy to fight the DUI charge. Based on Officer Joe's improper timing of the Miranda warning, the judge throws out Lucy's answers to his questions. Lucy's lawyer is then able to negotiate a DUI plea bargain to the reduced charge of "wet reckless."

Call us for help...


If you or a loved one has been accused of DUI and you are looking for strong legal defenses to DUI charges, we invite you to contact us at Shouse Law Group for a free in-person or telephone consultation. Our California DUI law offices are located in and around Los Angeles, Orange County, San Diego, Riverside, San Bernardino, Ventura, San Jose, Oakland, the Central Valley, the San Francisco Bay area, and several nearby cities.

Additionally, our Nevada DUI defense attorneys represent clients accused of violating Nevada's DUI laws. For information on Nevada DUI defenses, you can read our article on Nevada DUI defenses.

Legal References:

  1. Vehicle Code 23152(b) VC -- Driving with a BAC of 0.08 or above [per se definition of "intoxication" under California DUI law]. ("(b) It is unlawful for a person who has 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle.")
  2. Vehicle Code 23152(a) VC -- Driving under the influence [key to DUI defense of not actually being under the influence or impaired]. ("(a) It is unlawful for a person who is under the influence of any alcoholic beverage to drive a vehicle.")
  3. See, e.g., Vehicle Code 23536 VC -- DUI penalties for first offense.
  4. Vehicle Code 23152(a) VC -- Driving under the influence [key to DUI defense of not actually being under the influence or impaired], endnote 2 above.
  5. NHTSA, The Visual Detection of DWI Motorists, at 4.
  6. American Prosecutors Research Institute, Overcoming Impaired Driving Defenses, at 6.
  7. California Jury Instructions, Criminal. CALJIC 16.831 Alcohol or Drug Influenced Driving- Vehicle Code 23152(a) "Under the Influence"-Defined [legal definition of DUI is a key part of fighting DUI charges]. ("A person is [under the influence of an alcoholic beverage] [under the influence of a drug] [under the combined influence of an alcoholic beverage and a drug] when as a result of [drinking such alcoholic beverage] [and] [using a drug] [his] [her] physical or mental abilities are impaired to such a degree that [he] [she] no longer has the ability to drive a vehicle with the caution characteristic of a sober person of ordinary prudence under the same or similar circumstances.")
  8. See Manual of the Los Angeles Police Department, Volume 5, at 532 (describing Form 5.2.5 for DUI arrests].
  9. Standardized Field Sobriety Test (SFST) Validated at BACS Below 0.10 Percent, Mar. 1999. 
  10. Title 17 of the California Code of Regulations, section 1219.3 -- Breath Collection [basis of DUI defense challenging 15-minute observation period before a breath test]. ("A breath sample shall be expired breath which is essentially alveolar in composition. The quantity of the [California DUI] breath sample shall be established by direct volumetric measurement. The breath sample shall be collected only after the subject has been under continuous observation for at least fifteen minutes prior to collection of the breath sample, during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked.")  
  11. Title 17 of the California Code of Regulations, Sections 1215-1221 [failure to comply with these regulations can be the basis of an effective defense against California DUI charges].
  12. Burbank DUI defense attorney John Murray is a leading expert in California DUI defense, including the top 10 legal defenses to California DUIs and more obscure defenses. He has extensive experience both in the court systems of Los Angeles County and Ventura County and in California DMV hearings.


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