WASHINGTON: The National Highway Traffic Safety Administration (NHTSA) on Wednesday asked Tesla Inc to recall 158,000 Model S and Model X vehicles over media control unit (MCU) failures that could pose safety risks by leading to touchscreen displays not working. The auto safety agency made the unusual request in a formal letter to Tesla after upgrading a safety probe in November, saying it had tentatively concluded the 2012-2018 Model S and 2016-2018 Model X vehicles 'contain a defect related to motor vehicle safety.' Tesla did not immediately respond to a request for comment but it must respond to NHTSA by Jan. 27. If it does not agree it must provide the agency 'with a full explanation of its decision.' It is unusual for the agency to formally demand a recall. Automakers typically voluntarily agree to a recall if sought in discussions by regulators. The agency said it sought the recall after considering 'Tesla’s technical briefing presentation ... and evaluated Tesla’s assertions.' NHTSA added that 'during our review of the data, Tesla provided confirmation that all units will inevitably fail given the memory device’s finite storage capacity.' NHTSA said other automakers have issued numerous recalls for similar safety issues, the agency told Tesla, including a detailed list of prior callbacks. The agency said touchscreen failures pose significant safety issues, including the loss of rearview/backup camera images. It noted nine prior recalls by other automakers for similar problems. The Tesla vehicles that lose touchscreen use may see driver assistance Autopilot system and turn signal functionality impacted due to potential loss of audible chimes, driver sensing, and alerts associated with these vehicle functions, NHTSA said. It added that loss of alerts tied to systems like Autopilot 'increases the risk of a crash occurring because drivers may be unaware of system malfunctions.' Touchscreen failures result in drivers being unable to use windshield defogging and defrosting systems that 'may decrease the driver’s visibility in inclement weather, increasing the risk of crash.' NHTSA noted that 'Tesla has implemented several over-the-air updates in an attempt to mitigate some of the issues ... but tentatively believes these updates are procedurally and substantively insufficient.' It noted that under law 'vehicle manufacturers are required to conduct recalls to remedy safety-related defects.' NHTSA said in November it reviewed 12,523 claims and complaints about the issue, which would impact roughly 8% of the vehicles under investigation. Many complaints said Tesla requires owners to pay to replace the unit once warranties expire.