A fault detection method for a multi-phase motor system applies a first duty cycle to first phase coil windings and applies a second duty cycle to second phase coil windings. The second duty cycle differs from the first duty cycle by a first difference value D1. A first current I1 is measured. A third duty cycle is applied to third phase coil windings and a fourth duty cycle is applied to the second phase coil windings. The fourth duty cycle differs from the third duty cycle by a second difference value D2. A second current I2 is measured. Line-to-line resistances R1, R2 are calculated using the difference values D1, D2, the measured currents 11, I2, and a measured DC voltage VDC. After determining a resistance difference ΔR between the line-to-line resistances R1, R2, a comparison to a first non-zero threshold T1 indicates a fault.