A leading U.S. auto safety regulator on Friday announced an investigation into 73,000 Chevrolet Volt plug-in hybrid cars over reports that they may abruptly lose power, fail to restart and encounter other issues.

The National Highway Traffic Safety Administration said it’s opening a preliminary investigation into the model year 2016 through 2019 Chevrolet Volt amid complaints about the hybrid’s battery energy control module, or BECM. Some of the complaints indicated that drivers had little to no warning before the car lost operating power or entered reduced power mode.

NHTSA said the problem could pose a safety risk if vehicles can’t move with the flow of surrounding traffic and is more serious if a stalled vehicle is unable to restart.

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Some Chevrolet Volt owners have told NHTSA they faced months-long waits for replacement battery modules, and in some cases have been unable to obtain the replacement part. General Motors, the parent company of Chevrolet, said it has sufficient replacement parts in its supply pipeline.

One owner in Los Angeles said the Volt they were driving "suddenly, and unexpectedly lost propulsion while driving. The vehicle is no longer able to turn on or drive."

Another owner said the Volt couldn’t drive more than 35 mph while on the highway "and it stops driving on electricity randomly."

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GM previously issued a technical service bulletin that said if vehicles fail to restart the BECM may have to be replaced and reprogrammed, but the company hasn’t recalled the vehicles, NHTSA said.

The company indicated it’s cooperating with the NHTSA investigation and said it has "taken appropriate action to remedy customer concerns related to the battery energy control module but will continue to support the agency’s review of the matter."

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GM ended production of the Chevrolet Volt in early 2019.

Reuters contributed to this report.