Zero Motorcycles is recalling 2013 FX and 2012-2013 XU, S and DS models because of a problem with its controller firmware that could cause a motorcycle to suddenly shut down.

According to documents released by the National Highway Traffic Safety Administration, the controller firmware on some models may disconnect power to the motor in response to certain signal faults. The faults are random, infrequent and unrelated to the controller module, and should not affect the motorcycle function, so the controller should disregard them instead of reacting by cutting off power.

Ironically, the controller and firmware were initially installed to correct a separate recall campaign on 2012 S and DS models related to a sudden engine shut-down. That issue was caused by a motor encoder position signal drift outside the signal limits recognized by the motor controller.

After Zero received reports of similar sudden engine shut-downs, it discovered they were caused by those unrelated system faults. Zero Motorcycles personnel traveled to England to meet with Sevcon Limited, the manufacturer of the controller and firmware. Together, they concluded the signal faults were unavoidable during the life of a motorcycle, but the controller firmware should deal with them in a way that doesn’t result in the motor shutting down.

Zero dealers will update the firmware on affected vehicles so that they will be better able to respond to these random faults.