Products Liability Law Daily Wrap Up, DESIGN AND MANUFACTURING DEFECTS—MOTOR VEHICLES—Ariz. Sup. Ct.: Arizona Supreme Court restores two-part test for strict product liability in Toyota lane departure warning case, (Jul 9, 2026)

By Wendy Biddle, J.D.

Ruling clarifies that "defective" and "unreasonably dangerous" are separate elements a plaintiff must independently prove.

The Arizona Supreme Court held that a strict product liability claim requires proof of two distinct elements; that a product was defective, and separately, that the defect rendered it unreasonably dangerous. The ruling cleared up conflicting appeals court decisions that had declared that satisfying either the consumer expectation test or the risk/benefit analysis, established both defective condition and unreasonable danger; essentially eliminating the distinction. In so ruling, the Arizona Supreme Court vacated an appeals court decision that had allowed a design-defect claim against Toyota over a 2019 4Runner's lack of a lane departure warning system to proceed to trial, and affirmed the trial court’s award of summary judgment in favor of Toyota (Maywald v. Toyota Motor Corp., No. CV-25-0009-PR (Ariz. Sup. Ct. July 7, 2026)).

Background. The case arose from a December 2019 collision when a northbound driver fell asleep, crossed the center line, and struck the southbound vehicle of the plaintiff, seriously injuring the plaintiff. The injured sued Toyota Motor Corporation, Toyota Motor North America, and Overtyme, Inc., alleging strict liability for design defect, negligent design, and loss of consortium. Their theory centered on the 2019 4Runner's lack of a lane departure warning (LDW) system, technology that alerts a driver who begins drifting out of a lane. Toyota did not offer LDW, standard or optional, on that model.

The state trial court granted summary judgment for Toyota, concluding the vehicle was neither defective nor unreasonably dangerous and that its design did not cause the accident. The state appeals court vacated that ruling, holding that the consumer expectation test did not apply because LDW was not yet widely known or expected by ordinary consumers, but that the risk/benefit analysis applied without requiring a threshold showing of defect. Applying that analysis, the appellate court weighed the risks of omitting LDW against the benefits of including it and found triable issues of fact, reinstating the plaintiffs' claims. The Arizona Supreme Court granted review to resolve the elements of a strict product liability claim and clarify application of the consumer expectation and risk/benefit tests.

Strict liability. The court traced the strict liability doctrine to O.S. Stapley Co. v. Miller, 103 Ariz. 556 (1968) and its adoption of Restatement (Second) of Torts § 402A, later reinforced by Byrns v. Riddell and Rogers v. Unimac Co., which required proof both that a product was defective and that the defect made it unreasonably dangerous. The court noted that later intermediate appellate decisions had improperly collapsed these two elements into a single inquiry, and the court disapproved those decisions, along with any language in Dart v. Wiebe Mfg., Inc. 147 Ariz. 242 (1985) that blurred the distinction.

A plaintiff must first prove that the product was defective. The court explained that a "defective condition" exists when a product is unsafe for normal handling and consumption. While a product is "unreasonably dangerous" when it is more dangerous than a consumer would expect or when its risks outweigh its benefits. The consumer expectation test and risk/benefit analysis, the court clarified, are tools for assessing only the second element, unreasonable danger, not substitutes for proving a defect exists at all.

Applying that framework, the court concluded the 4Runner was not defective. Ordinary consumers expect vehicles to allow driving within marked lanes, but do not expect a vehicle to prevent driver error, including falling asleep at the wheel. Fundamentally, the driver’s responsibility is to maintain control of the vehicle, and the existence of the LDW technology does not eliminate that fundamental responsibility. The court cited Arizona's statutory duty on drivers to maintain their lane, A.R.S. § 28-729(1), and reasoned that the absence of an available safety feature does not itself establish defectiveness. Because the absence of the LDW technology did not render the 4Runner unsafe for ordinary use, the court concluded that the vehicle was not defective.

Because the plaintiffs could not establish defectiveness, their negligent design and derivative loss of consortium claims also failed. The court further clarified, though it found the issue unnecessary to its holding, that the risk/benefit analysis examines only the risks and benefits inherent in the product's actual design as sold, not a comparison to an alternative design incorporating additional safety technology.

Therefore, the court held that a plaintiff asserting strict product liability must first establish that a product was sold in a defective condition, and only then determine whether that defect rendered the product unreasonably dangerous. The court affirmed summary judgment for Toyota, concluding the plaintiffs failed to establish the threshold defect element, and vacated the court of appeals' memorandum decision.

The case is No. CV-25-0009-PR.

Judge: Beene, J.

Attorneys: G. Lynn Shumway (Shumway Law, PLLC) for Shawn Maywald. James W. Halbrooks (Bowman and Brooke LLP) for Toyota Motor Corp., Toyota Motor North America, Inc. and Overtyme, Inc.

Companies: Toyota Motor Corp.; Toyota Motor North America, Inc.; Overtyme, Inc.

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