--- title: "Why Did the Officer Make Me Blow Twice? California's Two-Sample Breath Test Rule" description: "California regulations require two separate breath samples that agree within 0.02. Being asked to blow more than twice usually means something went wrong with the test, and that matters more than most people realize." url: "https://www.thehfirm.com/blog/why-officer-made-me-blow-twice-breath-test" site: "H Law Group" published: "2026-07-28T09:00:00.000Z" --- # Why Did the Officer Make Me Blow Twice? California's Two-Sample Breath Test Rule California regulations require two separate breath samples that agree within 0.02. Being asked to blow more than twice usually means something went wrong with the test, and that matters more than most people realize. Category: DUI Law Author: Marshall Korns -- Marshall Korns manages client operations at The H Law Group, helping ensure every California criminal defense and DUI case receives responsive, professional, and client-focused support. If an officer had you blow into a breath machine two times, that was not the officer being thorough or trying to catch you out. It is what California regulations require. A single breath reading is not a valid test in this state. If you were asked to blow three, four, or five times, that is a different situation. It usually means the first attempts did not produce a usable result, and the reason they failed can matter a great deal to your case. Here is what the rule actually says, why the two readings have to agree, and what it signals when they do not. ## Two samples, and they have to agree within 0.02 California Code of Regulations, Title 17, section 1221.2 sets the standard: "For each person tested, breath alcohol testing shall include analysis of 2 separate breath samples which result in determinations of breath alcohol concentrations which do not differ from each other by more than 0.02 grams per 210 liters of breath." You can read the [text of section 1221.2](https://www.law.cornell.edu/regulations/california/17-CCR-1221.2) directly. Two things follow from that sentence. The test is not one reading, it is two. And the two readings have to land within 0.02 of each other to count as a valid test. So a 0.09 followed by a 0.10 is a valid pair. A 0.09 followed by a 0.12 is not. The machine is supposed to reject that second pair and the operator is supposed to start over. One note on citations, because this trips up a lot of people researching their own case. This requirement used to live in section 1219.3. That section was repealed and the rule moved to 1221.2 in a set of amendments operative April 1, 2017. Plenty of articles still cite the old number. If you are reading something that points you to 1219.3, it is working from an outdated version of the regulations. ## Why the agreement requirement exists at all A breath machine does not measure the alcohol in your blood. It measures alcohol in a sample of your breath and converts that to an estimated blood alcohol concentration using a fixed ratio. That conversion assumes a lot about the person breathing into it. The two-sample rule is a crude but real check on that estimate. If the machine is working correctly, if the operator is running it correctly, and if nothing in your mouth or lungs is interfering, two samples taken minutes apart should produce close to the same number. When they do not, one of those assumptions has failed. The regulation does not care which one. It just says the result is not valid. ## What it means if you blew more than twice Being asked for extra samples generally comes down to one of a few things. - The two readings were more than 0.02 apart, so the pair was invalid and the operator started again. - You did not blow long or hard enough to give the machine a deep lung sample, and it registered an insufficient sample rather than a reading. - The machine flagged an error, such as detecting alcohol in the surrounding air or an interfering substance. - You were given a roadside handheld test first and then a second, different test at the station. Those are two separate tests, not one test with extra blows. That last one accounts for a lot of the confusion. The roadside device and the station machine are different instruments used for different purposes, and being asked to blow into both is normal rather than a sign that something went wrong. ## The roadside test and the station test are not the same thing The handheld device an officer carries in the field is a preliminary alcohol screening device, usually called a PAS. For most drivers over 21 who are not on DUI probation, the PAS is a voluntary field sobriety test. The officer is supposed to tell you it is optional and that you can decline it. The test that comes after an arrest is a different matter. Under California's implied consent law, once you are lawfully arrested for DUI you are required to complete a chemical test of breath or blood, and refusing carries its own license consequences on top of whatever happens in the criminal case. Two exceptions matter. Drivers under 21 and drivers already on DUI probation are required to submit to the PAS as well. For everyone else, the roadside device is optional and the post-arrest test is not. ## What a wide split between readings can indicate When two samples disagree by more than the regulation allows, defense attorneys look at a handful of usual explanations. - Mouth alcohol. Alcohol trapped in the mouth or throat from a recent drink, a burp, acid reflux, or dental work reads far higher than deep lung air. Title 17 requires a continuous observation period before the test partly to rule this out. - Rising blood alcohol. If you were still absorbing alcohol at the time of the stop, your level may genuinely have been climbing between samples, which raises a separate question about what your level was when you were actually driving. - Instrument calibration and maintenance. Title 17 sets accuracy checks at defined intervals, and the records showing those were performed are discoverable. - Operator procedure. The person running the machine has to be trained and has to follow the required steps, including the observation period. A Title 17 problem does not automatically mean the reading gets thrown out. In practice, showing the regulations were not followed shifts the argument. It gives the defense a basis to challenge how much weight the number deserves, and it can matter at the DMV hearing as much as in criminal court. ## Do not let the 10-day DMV clock run out while you look into this A DUI arrest starts two separate cases. The criminal case has its own schedule, and the DMV license suspension runs on a much shorter one. Under [Vehicle Code section 13558](https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=13558.), the request for a DMV hearing has to be made within 10 days of receiving the notice of suspension. That hearing is where breath test problems often get their first real airing, because the license question turns heavily on the reading. Missing the deadline generally forfeits the hearing entirely. ## Frequently Asked Questions ### Is it normal to blow into a breathalyzer twice? Yes. Two samples are what the regulation requires, and the two results must be within 0.02 of each other. A single reading is not a complete breath test under California standards. ### What if my two readings were more than 0.02 apart? That pair does not satisfy the regulation. The operator should have run the test again. If the discrepancy appears in the records and was not addressed, it is worth having an attorney review the printout and the maintenance logs. ### Can I refuse the roadside breath test in California? If you are 21 or over and not on DUI probation, the preliminary roadside device is generally voluntary. The chemical test after a lawful arrest is not, and refusing that one carries separate license consequences. ### Does a Title 17 violation get my case dismissed? Not automatically. It gives the defense a documented basis to challenge the reliability of the reading. How much that is worth depends on the specific violation and what else is in the case. ### Should I have chosen a blood test instead? Each has trade-offs. A blood sample can be preserved and independently retested later, which a breath sample cannot. Breath results come back immediately. Which is better depends on the facts, and it is not a decision that can be usefully made in the abstract. ## About the author Marshall Korns is an attorney with H Law Group, a California criminal defense and DUI firm representing clients across Los Angeles and throughout the state. His practice includes DUI defense, DMV administrative per se hearings, and challenges to chemical test evidence. > This article is general information about California law, not legal advice about your situation. Breath testing regulations and DUI procedure are amended from time to time, and how any rule applies depends on the specific facts of a case. 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