The Consumer Financial Protection Bureau has proposed bringing the financing units of the big automakers under federal supervision for the first time, a move that would let the agency examine the lending arms of Toyota, Ford and Honda. The bureau has grown concerned that some car buyers are being steered into expensive loans when they qualify for cheaper ones and being misled about the terms and benefits of add-on products. The proposed rule would extend the bureau’s current oversight of bank auto lenders to cover 38 auto finance companies that make, acquire or refinance 10,000 or more loans or leases a year. The firms provided financing to about 6.8 million consumers last year.