NEW YORK (AP) -- Tesla knocked roughly a third off the price of its "Full Self Driving" system -- which can't drive itself and so drivers must remain alert and be ready to intervene -- to $8,000 from $12,000, according to the company website.

Tesla CEO and billionaire Elon Musk promised in 2019 that there would be a fleet of robotaxis on the road in 2020, but the promise has yet to materialize, and the system still has to be supervised by humans.

The cuts, which occurred on Saturday, follow Tesla's moves to slash $2,000 off the prices of three of its five models in the United States late Friday. That's the latest evidence of the challenges facing the electric vehicle maker.

Tesla reduced the prices of the Model Y, a small SUV which is Tesla's most popular model and the top-selling electric vehicle in the U.S., and also of the Models X and S, its older and more expensive models. Prices for the Model 3 sedan and the Cybertruck stayed the same.

The price reduction came the day after Tesla's stock dropped below $150 per share, wiping out all gains made over the past year. The Austin, Texas, company's stock price has dropped about 40% so far this year amid falling sales and increased competition. Discounted sticker prices are a way to try to entice more car buyers.