Tesla Inc. badly missed its goal of building 1,500 Model 3 cars in the third quarter, the first sign that the production ramp-up for the new sedan isn’t going as smoothly as planned.

The Silicon Valley electric-car maker built 260 of the Model 3s between July and September, the company said Monday in a statement. In August, the auto maker predicted it would build more than 1,500 Model 3s before cranking up production to 5,000 a week by the end of the fourth quarter.

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