Driver assistance systems support overstrained and affected drivers and become more and more essential for series-production vehicles. In this paper a procedure for detection of a misaligned or blocked sensor system, including a radar and a camera sensor, will be introduced. It is important to inform the driver if an automatic headlight control is working reliable, in other words without limitations caused by external influence (e.g. dirt on the windscreen). The blockage detection algorithm is based on the fusion result of electronic radar measurements and a vision based head- and taillight detection algorithm. Results of the blockage detection algorithm are evaluated on misaligned measurements and online in a vehicle test system.