In Cooper v. State Farm Mutual Automobile Ins. Co. (2009) 177 Cal.App.4th 876, the Court of Appeal held a duty to preserve evidence existed based on an express promise to preserve the evidence. Cooper involved a single-vehicle car accident allegedly caused by the tread separating from one of the vehicle's tires. The driver's insurance company, State Farm, took possession of the vehicle and the tire after settling the driver's property damage claim. State Farm hired an expert who examined the vehicle and concluded the tire was defectively manufactured. (Cooper, supra, 177 Cal.App.4th at pp. 879, 881-882.) State Farm shared this information with the driver, who hired counsel and filed a product defect action against the tire manufacturer. The driver's counsel repeatedly wrote State Farm emphasizing the tire's critical importance as evidence, and warning State Farm its failure to preserve the tire would subject it to liability for spoliation. State Farm expressly promised to preserve the tire on three occasions. But, after foregoing a subrogation claim, State Farm sold the vehicle and tire as scrap. The driver sued State Farm, alleging he could not reasonably prevail on his claim against the tire manufacturer without the tire. (Cooper, supra, 177 Cal.App.4th at pp. 880, 882-883, 884-885, 888.) The trial court granted nonsuit for State Farm following the driver's opening statement, concluding Cedars-Sinai and Temple barred the driver's claim. (Cooper, supra, 177 Cal.App.4th at p. 880.) The Court of Appeal reversed: "Here, rather than seeking to impose a general tort duty of care on State Farm to preserve evidence, plaintiff, during his opening statement, presented prima facie facts to support an independent duty to preserve the tire based on State Farm's promise and plaintiff's reliance thereon. As stated in Coprich v. Superior Court (2000) 80 Cal.App.4th 1081, while there may be no general tort duty to preserve evidence, this 'does not preclude the existence of a duty based on contract.' The general tort duty 'policy considerations do not negate the existence of a contractual obligation created by mutual agreement or promissory estoppel.' Additionally, ' "it is ancient learning that one who assumes to act, even though gratuitously, may thereby become subject to a duty of acting carefully, if he acts at all." ... "... 'If the defendant enters upon an affirmative course of conduct affecting the interests of another, he is regarded as assuming a duty to act, and will thereafter be liable for negligent acts or omissions.' " Thus, it is settled law that one "who, having no initial duty to do so, undertakes to come to the aid of another ..." ... has "a duty to exercise due care in performance and is liable if ... the harm is suffered because of the other's reliance upon the undertaking." ' " (Cooper, supra, 177 Cal.App.4th at p. 894.)