A vehicle includes an electric machine and a controller configured to inject a voltage into the electric machine. The controller measures the currents caused by the voltage and processes the currents using a discrete Fourier transform to determine positive and negative sequence currents. A phase rotation sequence is identified by comparing the sequence currents to expected positive and negative sequence currents that are associated with possible phase rotation sequences. The electric machine may be controlled according to the identified phase rotation sequence. A cable swapped diagnostic may be output when the phase rotation sequence is different than an expected phase rotation sequence.