Editor's note: The NHTSA investigation involves the vehicles' media control unit. The type of unit was misstated in an earlier version of this story.
WASHINGTON -- The National Highway Traffic Safety Administration said on Monday it was upgrading a probe into nearly 159,000 Tesla Model S and Model X vehicles over touchscreen failures to an engineering analysis.
The auto safety regulator had opened a preliminary evaluation in June. The NHTSA said the failure can result in the loss of rear-camera image display when in reverse and reduced rear visibility when backing up, and can impact defogging ability, and audible chimes relating to Autopilot and turn signals.
Tesla did not respond to a request for comment.
NHTSA can order a recall of a vehicle following an engineering analysis.
The probe now covers 2012-2018 model year Tesla Model S and 2016-2018 Model X vehicles. The preliminary investigation covered 63,000 Tesla Model S cars.
NHTSA said the failure does not affect vehicle-control systems.
The media control unit uses an Nvidia Corp. Tegra 3 processor, NHTSA said.
The flash devices have a finite lifespan based on the number of programs or erase cycles, NHTSA said.
Some complaints said failures could result in loss of charging ability and that other safety alerts could be impacted. One driver said he could not clear fogged windows because he could not change climate controls.
In total, NHTSA said it has reviewed 12,523 claims and complaints about the issue, which would impact roughly 8 percent of the vehicles under investigation.
Tesla said it has received 2,399 complaints and field reports, 7,777 warranty claims, and 4,746 non-warranty claims related to MCU replacements.
Many complaints said Tesla requires owners to pay to replace the unit once warranties expire.
NHTSA said the data showed "failure rates over 30 percent in certain build months and accelerating failure trends after 3 to 4 years-in-service." Tesla has implemented over-the-air updates "to mitigate the effects of MCU failure," NHTSA said, including changes to reduce memory usage of the subject memory card, improving storage management strategies, and changing the control logic for turn signal activation.