Many of the processors used in automotive Electronic Control Units (ECUs) are resource constrained due to the cost pressures of volume production; they have relatively low clock speeds and limited memory. Controller Area Network (CAN) is used to connect the various ECUs; however, the broadcast nature of CAN means that every message transmitted on the network can potentially cause additional processing load on the receiving nodes, whether the message is relevant to that ECU or not. Hardware filters can reduce or even eliminate this unnecessary load by filtering out messages that are not needed by the ECU. Filtering is done on the message IDs which are primarily used to identify the contents of the message and its priority. In this paper, we consider the problem of selecting filter configurations to minimize the load due to undesired messages. We show that the general problem is NP-complete. We therefore propose and evaluate an approach based on Simulated Annealing. We show that this approach nds near-optimal filter configurations for the interesting case where there are more desired messages than available filters.