How breath test results are challenged in Michigan OWI cases

A breath test result in a Michigan drunk-driving (OWI) case is challenged by testing it against the legal requirements the test had to meet: an approved and maintained instrument, a certified operator, a 15-minute observation, and properly matched samples.^[4][5][6][7] The result is admissible and is presumed to equal the driver's level at the time of driving, but the jury decides how much weight it deserves and is told to consider the equipment, the procedure and the operator's training.^[1][13][2]

This page describes those requirements and what Michigan courts have said happens when they are not met. It is not a guide to avoiding or defeating a test. The roadside preliminary breath test (PBT) has its own rules and limited uses, covered in the roadside preliminary breath test.

Where the breath-test rules come from

The Vehicle Code directs the Department of State Police to make uniform rules for administering chemical tests.^[3] Those rules (Mich Admin Code R 325.2651 and following) were last amended in 2023; "department" now means the State Police, and two older rules were rescinded.^[14]

The rules require evidential and preliminary breath instruments to meet the National Highway Traffic Safety Administration's model specifications, and operators may use only equipment the State Police have approved.^[4] Michigan's current evidential instrument is the Intoxilyzer 9000.^[15] For its history, including the 2020 DataMaster service-record case, see the station breath test machines.

The requirements a breath test must meet

Requirement	What the rule says
Certified operator	An evidential test is run by a Class III operator; Class III operators certified after January 1, 2022 must recertify every 2 years.[16][5]
Training and exam	Class III certification requires Class II certification, an approved course, at least 70% on a written exam, and demonstrated proficiency on an evidential instrument.[17]
Observation	At least 15 minutes of observation by a certified operator before the sample, with no smoking, regurgitating or anything in the mouth except the mouthpiece.[6]
Two samples	A second sample is requested after the first is analyzed, unless something that could interfere is found in the mouth; the first result alone meets evidentiary requirements, and the second confirms it.[18]
Agreement between samples	The second result must fall within a set tolerance of the first, from plus or minus 0.01 at low readings up to plus or minus 0.04 at 0.35 or more.[7]
Standard check during the test	If the instrument tests a known ethanol standard during the subject's test, that reading must be between 0.074 and 0.084 g/210 L.[19]
Accuracy checks	Instruments that do not test a known standard with each subject must be checked at least weekly and read within plus or minus 5% of a 0.080 standard.[8]
Inspection	Inspection within 120 days of the last one, or at least twice a year for instruments that test a known standard with each subject.[20]
Reporting the number	Results are expressed in grams per 210 liters of breath and truncated to two decimals (or three if the instrument is set to do so).[19]

This guide did not find an official page saying which inspection schedule applies to the Intoxilyzer 9000, so it does not say which one governs that machine.

The State Police may suspend an operator's certification for not following department rules, policies and procedures.^[21] A lapsed operator must retake the course but can still testify about tests given while certified.^[5] Not every rule affects validity: an operator must request medical help when a result is 0.35 or more, but failing to do so does not affect the result's validity or evidential value.^[22]

The 15-minute observation period

Several Michigan appellate cases discuss the observation rule. The current text, last amended in 2023, says the operator need not stare continuously but must be close enough to be aware of the person's actions and conditions, and that breaks of only a few seconds do not invalidate the observation if the operator can reasonably determine the person did not smoke, regurgitate or put anything in the mouth.^[6] The observation may be done by more than one operator working together.^[6]

A common misstatement is that any interruption voids the test. That is not what the rule or the cases say.^[6][10] The full rule and its history are on the 15-minute observation rule page.

What courts have done when a rule was not followed

Michigan appellate courts have looked at how serious the violation was and whether it called the result's accuracy into question:

• Boughner (1995). The operator watched the defendant for no more than eight minutes, not continuously, while video showed the defendant's hand on his face or in his mouth; the Court of Appeals held this undermined the result enough to reverse a plea-based conviction.^[11]
• Wujkowski (1998). A six-second gap while the operator checked the machine, with another officer present, was a de minimis, technical violation that did not require suppression.^[10]
• Robe (2021). A roadside PBT given after about three minutes of observation, with no one else watching for the rest, had to be excluded from the probable-cause analysis because the violation was significant and called the result's accuracy into question.^[9] On a later unpublished appeal, the court sent the case back to decide whether the good-faith exception applied.^[23]

Boughner and Wujkowski were decided in the 1990s under earlier versions of the rules, and the current text expressly tolerates breaks of a few seconds.^[10][14][6] Whether a particular violation leads to suppression is decided by the judge on the facts of the case; for how suppression motions work, see motions to suppress evidence.

Weight at trial: what the jury is told

Even when a result is admitted, the jury instruction lists the questions jurors are to ask: was the test technically accurate, was the equipment properly assembled and maintained and in good working order, was the test given correctly, and was the person who gave it properly trained.^[2] Jurors may infer that the level at the test equaled the level when driving, and may give the test whatever weight they believe it deserves.^[13]

The test is never the only evidence. The chemical-test provisions do not limit other admissible evidence on whether the person was impaired or had a 0.08 level.^[24] How the time between driving and testing is handled is covered in rising BAC and the time-of-driving question.

Getting the records

Two rules govern access to test information before trial:

1. On a written request to the prosecutor, with a copy filed with the court, the prosecution must furnish the chemical-test results at least 2 days before trial, and failure to fully comply bars the prosecution from using them.^[12]
2. Under the discovery rule, the prosecutor must provide on request any police report, the defendant's recorded statements, search warrant papers, and exculpatory information; the court may order non-destructive testing of tangible evidence for good cause.^[25] In a misdemeanor case, the part of the rule that includes this testing provision, MCR 6.201(A), applies only if the defendant elects to request discovery under it, and the defendant then has reciprocal duties.^[26]

The State Police also publish subject-test data for each Intoxilyzer 9000 by serial number, with personal information removed.^[27] Practical step: write down the date, time and place of the test and the names on any paperwork you received, so records can be matched later. For video and police records more generally, see discovery and video evidence.

The independent test

A person who takes the officer's chemical test must be given a reasonable opportunity, within a reasonable time after detention, to have a person of his or her own choosing give one of the chemical tests, and is responsible for getting that sample analyzed.^[28] The Court of Appeals has held that this does not let a defendant pick a particular State Police analyst or force the State Police lab to retest its own evidence.^[29] Details are on the right to an independent chemical test.

Common misunderstandings

• "The breath number is the end of the case." The result is admissible and presumed to reflect the time of driving, but jurors decide its weight and are told to consider maintenance, procedure and training.^[1][13][2]
• "Any procedural slip throws out the test." Courts have separated significant violations that call accuracy into question from de minimis ones.^[9][10]
• "The roadside PBT number will be used at trial." PBT results are admissible only to decide a challenge to the arrest or to rebut specific testimony about whether the level was higher or lower at the time of driving.^[30]

For the overall picture of OWI evidence, see the evidence in an OWI case.