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Consumer Reports magazine says it expects Toyota in January to announce plans to repair about 700,000 Lexus automobiles because the emergency trunk release can break, trapping an occupant inside.

The vehicles are the 2007-2013 Lexus ES, 2006-2012 Lexus IS, and 2013 Lexus GS models, according to the magazine, which brought the problem to the attention of the automaker and the National Highway Traffic Safety Administration.

Owners can thank 4-year-old Alexander Fisher for discovering the problem. Alexander is the son of Jake Fisher, director of automotive testing for Consumer Reports.

Mr. Fisher said his 4- and 9-year-old sons are fascinated by cars and the idea of testing them. Not long ago they convinced him they could help test the emergency trunk release — which is inside the trunk — with him standing nearby should things go awry.

In October, Alexander was in the trunk of a new Lexus ES 350. But instead of popping the trunk open, he asked his father to let him out.

The emergency handle had broken off when the 4-year-old pulled on it.

“He was there holding the piece of plastic in his hand,” Mr. Fisher said. “He thought it was funny.”

Mr. Fisher was less amused.

A check of another Lexus being tested by the magazine showed the same flaw: When the handle is pulled toward the driver’s side it breaks.

“It is very brittle and it snaps off,” Mr. Fisher said.

Mr. Fisher wrote a blog post about it and the magazine contacted Toyota and traffic safety administration.

A Toyota spokesman could not immediately be reached for comment.

Consumer Reports says the automaker will conduct a service campaign, which means the vehicles will be repaired for free.

But Clarence Ditlow, the executive director of the Center for Auto Safety says that’s not enough.

“Trunk releases are safety features designed to free trapped occupants,” Mr. Ditlow wrote in an e-mail. “Toyota should conduct a safety recall.”

Consumers are more likely to have the repair made for a recall than a service campaign, he said.

A recall also has legal requirements, include a rule that the automaker must report completion rates to the safety agency.

Asked why a recall was not warranted, Karen Aldana, a spokeswoman for the N.H.T.S.A., wrote in an e-mail that the agency will “monitor the issue and will take appropriate action as warranted.”

Mr. Fisher said Consumer Reports hasn’t taken a position on whether a recall is needed.

“Consumer Reports applauds Toyota for quickly addressing the problem and making the necessary fix to ensure that if someone does get trapped in a trunk, they can safely and easily escape without incident,” the magazine said in a statement.