Tesla faces the potential for one of the most expensive recalls in automotive history as it prepares to replace self-driving computers in about 4 million vehicles, according to Electrek. The company previously claimed that all vehicles produced after 2016 had the hardware required for full self-driving. Still, CEO Elon Musk recently admitted the computer cannot support unsupervised autonomous driving. Owners who paid thousands for Tesla's Full Self-Driving package will be eligible for a retrofit, which Musk called “painful and difficult.” Tesla has not disclosed how many customers bought the package.