There has been an increasing interest in developing a reliable sensor to guard automotive DC motors from an unexpected current surge. We have developed self-resettable positive temperature coefficient (PTC) sensors from two polymer PTC material systems for this purpose. One is a polyolefin based conductive material which provides a switch temperature of around 125°C. The other is a polyamide based material with a higher switch temperature of 165°C for applications where ambient temperature is typically higher. Presented herein are operation principles and material PTC characteristics of the newly developed self-resettable protection sensors. Performance of these sensors is also discussed.