This is a method of determining a fault with a vehicle spray device e.g. screen washer, particularly for autonomous vehicles e.g.in a platoon, where a fault cannot be determined manually by a driver. The method actuates a spray device on a first vehicle 1025 and receives an image, from a second vehicle 1035, of the actuated spray device. It is determined whether a spray device fault or problem exists based at least on the image of the actuated spray device 1045. The fault is transmitted via a first vehicle communications network. If a fault exists, the first vehicle may be navigated to a service facility 1-65. The second vehicle may take images of the spray device before and after actuation to determine the fault. The method may also indicate if there is a fault with a camera on the first vehicle if images are below a required quality. The cameras on the vehicles may be operated upon request 1015, 1030 from other vehicles.