Method and arrangement for providing a compressed air system in a vehicle that includes a connection (6, 10) for delivering compressed air from a compressor (2) to the rest of the compressed air system (1). An oxidation catalytic converter (9) is included that is designed to clean the compressed air and which is located along the connection (6, 10). The connection (6, 10) includes a line (10) that forms a connection between the oxidation catalytic converter (9) and the rest of the compressed air system. The invention also includes a valve (11) that is arranged upstream of the rest of the compressed air system (1) and that can be adjusted so that in a first position it will allow and in a second position will prevent the delivery of air to the rest of the compressed air system (1), depending on the operating condition of the compressor (2). The invention provides an improved system in which the risk of contaminated air being delivered to the compressed air system is minimized.