Mobile nodes are organized randomly without any access point in Mobile Ad hoc Networks (MANETs). Due to the mobility of nodes, the network congestion occurs. So many congestion control mechanisms were proposed to avoid the congestion avoidance or reducing the congestion status. In this research work, we proposed to develop the Effective Congestion Avoidance Scheme (ECAS), which consists of congestion monitoring, effective routing establishment and congestionless based routing. The overall congestion status is measured in congestion monitoring. In routing establishment, we propose the contention metric in the particular channel in terms of, queue length of packet, overall congestion standard, packet loss rate and packet dropping ratio to monitor the congestion status. Based on the congestion standard, the congestionless based routing is established to reduce the packet loss, high overhead, long delay in the network. By extensive simulation, the proposed scheme achieves better throughput, packet delivery ratio, low end-to-end delay and overhead than the existing schemes.