Retarder　is　an　auxiliary　braking　device　of　vehicles　which　can　improve　the　reliability　and　extend　the　lifespan　of　the　vehicle　braking　system,　by　means　of　reducing　maintenance　costs　greatly,　an　effective　retarder　can　also　enhance　the　comfort　of　vehicles.　This　paper　constructed　an　eddy　current　retarder　control　system　framework　with　CAN　bus,　and　designed　its　valid　layer　communication　and　fault　diagnosis　system,　based　on　protocol　SAE　J1939.　In　order　to　test　the　eddy　current　retarder,　we　designed　a　compliance　testing　computer　software,　including　corresponding　software　and　hardware.　After　the　test,　it　proved　that　the　eddy　current　retarder　control　system,　based　on　SAE　J1939,　works　stably　with　reliable　data　communication　favorable　real　time　control　and　convenient　malfunction　diagnosis.