marvelouzone
New member
2002 international 4300 throws code 521 according to servicemaxx, injector harness is new, suspecting ecm, but not sure if this could be a possible solution. all new clean power connections, swapped ecm relay, i get the 521 code even with injector harness disconnected during an injector test. removed wire looming from injector wires to ecm and see no signs of frayed or bad wires.. wanted to remove wire harness from ecm to do a pin/ohm test, but even after trying to back connectors off with 1/4" ratchet still couldnt pull harness loose from ecm, which is crazy because I've had them off before..