Abstract: Collision detection systems are commonly provided on automatic guided industrial vehicles. Such systems should be as reliable as possible and can advantageously utilize a fault detection apparatus. The subject apparatus provides a plurality of radiant energy emitting devices and receiving devices positioned along a vehicle at locations sufficient that an obstacle in a respective path of the vehicle interrupts the reception of radiant energy by respective ones of the receiving devices. Interruptable devices controllably connect a power supply to a brake control circuit in response to continuous reception of radiant energy by the respective receiving devices, and disconnect the power supply from the brake control circuit in response to any of the receiving devices failing to continue to receive radiant energy from the respective emitting device.