Tesla is suing a Swiss parts vendor that the electric-vehicle maker said produced a defective hydraulic system for the Model X's signature, vertically opening winged doors. Hoerbiger's prototype never was used in Tesla's latest electric car, and Tesla had to retool "the entire vehicle in order to support a different engineering solution," Tesla claims.

According to Tesla's lawsuit (PDF), filed Tuesday in San Francisco federal court:

On numerous occasions, Tesla notified Hoerbiger of the multitude of defects with its product. While Hoerbiger insisted it could fix the problems, Hoerbiger failed to do so. Instead, Hoerbiger provided a product that never came close to being ready for production. For example, the system was prone to overheating, which caused it to shut down—making the doors inoperable—when Tesla stress-tested a prototype vehicle. The doors also did not open with the speed or symmetry that Tesla required, including when a prototype vehicle was parked at an incline or when the system was exposed to extreme temperatures. Hoerbiger's doors also “sagged” beyond Tesla's specified tolerance levels. Furthermore, the product persistently leaked oil, both internally and externally, which, as Hoerbiger acknowledged, was entirely unacceptable, negatively impacting performance as well as leaving unsightly markings and stains inside the vehicle. In sum, Hoerbiger's prototype never came close to fulfilling the promises made by Hoerbiger. Ultimately, the deficiencies in Hoerbiger's product made it an unworkable engineering solution for the Falcon Wing doors of the Model X.

The hydraulics maker declined Ars' request for comment. But the suit, which seeks millions in damages, notes that the parties are disputing whether "Tesla was contractually obligated to purchase production parts from Hoerbiger and whether Hoerbiger is entitled to recover for Tesla's decision not to purchase such parts." Tesla said Hoerbiger's demands are "unreasonable."

Tesla, meanwhile, said in the lawsuit that it switched to "electromechanical parts, instead of hydraulic ones, and thus revised the engineering design of the Falcon Wing doors."

The suit says that, because of "Hoerbiger's negligence, Tesla incurred millions of dollars in damages."