California’s breathalyzer law treats every licensed driver as having already consented to a chemical test of breath or blood once lawfully arrested on suspicion of DUI. Blow a 0.08% or higher and you face DUI charges. Refuse the test after arrest and the DMV suspends your license for a year automatically, even if the criminal case later falls apart.1California Legislative Information. California Vehicle Code 23152 The rules around when you can refuse, which test counts, and how to protect your license run on tight deadlines, and a few of them are counterintuitive.
The BAC Numbers That Matter
The threshold depends on who you are and what you’re driving:
- Drivers 21 and older: 0.08%.1California Legislative Information. California Vehicle Code 23152
- Drivers under 21: 0.01% under California’s zero-tolerance law.2California Legislative Information. California Vehicle Code 23136
- Commercial drivers and anyone carrying passengers for pay: 0.04%.3State of California Department of Motor Vehicles. California Driver’s Handbook – Section 9: Alcohol and Drugs
- Drivers on DUI probation: 0.01%.3State of California Department of Motor Vehicles. California Driver’s Handbook – Section 9: Alcohol and Drugs
A reading at or above your limit, taken within three hours of driving, creates a rebuttable presumption that you were intoxicated. You can challenge it, but the burden shifts to you to explain the number.1California Legislative Information. California Vehicle Code 23152
Which Test You Can Actually Refuse
Vehicle Code 23612 is the implied consent statute. By driving in California, you have already consented to a chemical test of your breath or blood after a lawful DUI arrest.4California Legislative Information. California Vehicle Code 23612 Two words carry most of the weight: “lawfully arrested.” The officer needs probable cause, which can come from erratic driving, the smell of alcohol, or failed field sobriety tests.5Justia. CALCRIM No. 2130 – Refusal – Consciousness of Guilt After arrest you generally pick breath or blood. If the officer suspects drug impairment, you’ll be required to give blood, because breathalyzers only read alcohol.
The Roadside Handheld Is Different
The small device an officer pulls out at the roadside is a preliminary alcohol screening (PAS) device, not the evidentiary test implied consent covers. If you are 21 or older and not on DUI probation, you can decline the PAS without triggering refusal penalties.4California Legislative Information. California Vehicle Code 23612 Officers are supposed to tell you this, but the advisement sometimes gets missed in the moment.
Two groups don’t get that choice. Drivers under 21 and anyone on DUI probation are required to take the PAS, and refusing it carries the same penalties as refusing a post-arrest chemical test.2California Legislative Information. California Vehicle Code 23136
You Can’t Wait to Call a Lawyer
Asking to consult an attorney before deciding is treated as a refusal. The Sixth Amendment right to counsel hasn’t attached yet because formal criminal proceedings haven’t begun, and the courts have held that delaying the test to find a lawyer counts the same as saying no.
What a Refusal Costs
Refusing the post-arrest chemical test triggers two separate consequences, and they stack. One happens through the DMV. The other happens in criminal court if you’re convicted.
The Automatic License Action
The DMV penalties scale with your prior history in a ten-year window:
- First refusal: one-year suspension.6California Legislative Information. California Vehicle Code 13353 (2025)
- Second refusal within ten years: two-year revocation.6California Legislative Information. California Vehicle Code 13353 (2025)
- Third or subsequent within ten years: three-year revocation.6California Legislative Information. California Vehicle Code 13353 (2025)
This is a civil administrative action and it runs independently of the criminal case. If the district attorney drops the DUI charge, the refusal suspension still stands. Refusing also narrows your access to a restricted license that would let you drive to work or school during the suspension. Drivers with a third or subsequent DUI offense in ten years can’t get any restricted license.7California Department of Motor Vehicles. Driving Under the Influence (DUI)
Added Jail Time if You’re Convicted
Under Vehicle Code 23578, a judge can add jail time as a sentencing enhancement when you refused the test and are then convicted of DUI. A first DUI with refusal adds 48 hours. A second within ten years adds 96 hours. A third adds 10 extra days. Prosecutors also commonly argue the refusal itself to a jury as consciousness of guilt, meaning you declined because you knew you’d fail.5Justia. CALCRIM No. 2130 – Refusal – Consciousness of Guilt
You Have 10 Days to Request a DMV Hearing
This is the deadline that catches people. After the arrest, the officer takes your license and issues a temporary paper permit. The DMV will suspend your driving privilege 30 days later unless you request an administrative per se (APS) hearing within 10 days of receiving the suspension notice.8California Legislative Information. California Vehicle Code 13558
Miss that window and the suspension takes effect automatically with no hearing. There is essentially no path to revive the request afterward. At the hearing you can contest whether the stop was lawful, whether the arrest had probable cause, and whether the testing was done correctly. Winning sets aside the license action, though the criminal case continues on its own track.
Grounds to Challenge a Breath Result
California’s breath testing procedures are governed by Title 17 of the Code of Regulations, and every departure from protocol is a potential weakness in the state’s case.
Calibration and Operator Training
Each breathalyzer must be checked for accuracy against a known-concentration solution every 10 days or every 150 tests, whichever comes first. Readings taken from a device past either threshold are open to challenge, as are results from an officer who hasn’t completed the required training.9Cornell Law School. Cal. Code Regs. Tit. 17, 1221.2 – Standards of Procedure
The 15-Minute Continuous Observation
Before taking a sample, the officer must observe you continuously for 15 minutes. During that period you cannot eat, drink, smoke, vomit, or burp, because any of those can push residual alcohol from your stomach into your mouth and contaminate the sample.10Cornell Law School. Cal. Code Regs. Tit. 17, 1221.1 – Authorized Procedures “Continuous” is the operative word. If the officer walks away to handle paperwork and comes back, the observation wasn’t continuous and the result becomes challengeable.
Two Samples, Within 0.02
You must give two separate breath samples, and the results can’t differ by more than 0.02 grams of alcohol per 210 liters of breath. A wider gap suggests something went wrong and may require further testing.9Cornell Law School. Cal. Code Regs. Tit. 17, 1221.2 – Standards of Procedure
GERD and Mouth Alcohol
Breathalyzers measure air coming from your lungs, but they can’t distinguish lung air from alcohol vapor that rose up from your stomach. Gastroesophageal reflux disease (GERD) is the condition most often raised in defense of a high reading. People with GERD regularly experience stomach contents moving back into the esophagus and mouth, and documented case reports show breath test outputs with wavering concentration curves and negative slopes consistent with mouth-alcohol contamination rather than true lung-air alcohol. Proton pump inhibitors and GLP-1 drugs like semaglutide have been reported to increase reflux and burping around the time of testing.11NCBI. The Limitations of Mouth Alcohol Detection Systems in Breath Alcohol Testing: Case Reports The 15-minute observation is meant to catch this, but modern analyzers don’t always flag it. A documented GERD or reflux diagnosis and a current medication list can matter a great deal when challenging an elevated reading.
Extra Rules for CDL Holders
Commercial driver’s license holders live under a stricter version of these rules. The BAC limit in a commercial vehicle is 0.04%.3State of California Department of Motor Vehicles. California Driver’s Handbook – Section 9: Alcohol and Drugs And refusing a chemical test is a disqualifying offense under federal law, with or without a DUI conviction. A first offense carries a one-year disqualification from operating commercial vehicles; a second within three years brings a three-year disqualification.12eCFR. 49 CFR 391.15 – Disqualification of Drivers A one-year disqualification ends most trucking careers because employers rarely hold a seat that long.
Costs That Follow a Conviction
A DUI conviction brings expenses well beyond court fines. California requires an ignition interlock device on every vehicle you operate, with installation and monthly calibration fees that run past $1,000 over the required period.13California Legislative Information. California Vehicle Code 23575.3 You’ll also need to file an SR-22 certificate of financial responsibility with the DMV for three years from reinstatement, and insurance premiums climb accordingly; any coverage lapse during that period restarts the three-year clock. A state-licensed DUI education program is mandatory, running from three months for a first offense up to 30 months for repeat offenses. The conviction itself stays on your California driving record for 10 years.3State of California Department of Motor Vehicles. California Driver’s Handbook – Section 9: Alcohol and Drugs Professionals who hold state licenses or federal security clearances should check their reporting obligations right away; failing to disclose a DUI during a clearance investigation is often treated more harshly than the DUI itself.