PALO ALTO (CBS SF) – Consumer Reports magazine has lowered the ratings of Tesla’s Model S and Model X electric cars, after the automaker delayed the rollout of a safety feature promised to owners for the past several months.

According to the magazine, vehicles produced since October 2016 don’t have automatic emergency braking enabled, which uses sensors to slow down or stop a vehicle to avoid a crash.

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A study by the Insurance Institute for Highway Safety found the feature cut rear-end crashes by 40 percent.

Standard on previous Tesla models, the feature was not available to newer vehicles as the Palo Alto-based automaker placed second-generation hardware for the company’s Autopilot system.

Tesla promised the feature would become available to owners through a software update by the end of last year. However, Consumer Reports testers who purchased a Model S in December said their car did not have automatic emergency braking, despite four software updates and repeated questions to the automaker.

“When we purchased our latest test car, we were assured automatic emergency braking would be enabled by the end of 2016,” said Jake Fisher, who directs the magazine’s auto testing center.

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As a result, the magazine dropped the score of the Model S by two points, placing it behind the Lexus LS and BMW 7 Series in the “ultraluxury” category where it once led. The Model X also had its ratings drop in the luxury SUV category.

Tesla told the magazine the automatic emergency braking rollout has been delayed due to software issues and said it expects to send a software update with the feature to owners starting Thursday.

Consumer Reports said it would reevaluate their ratings once all affected owners receive the update and sells new vehicles with automatic emergency braking enabled.

Once a feature that appeared only in luxury cars, the feature is available in a growing number of lower-priced automobiles, including the Honda Civic and Toyota Corolla.

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Last year, the National Highway Traffic Safety Administration (NHTSA) and automakers announced automatic emergency braking would be standard in nearly all new vehicles sold in the U.S. by 2022.