Does not mark the speed

Good night. I am doing an Opel Corsa C, 1.0 3 cylinders engine, which does not mark the vehicle speed, specifically the mark sometimes, jumping the needle. I have made a diagnosis with my machine and gives me a breakdown in the speed sensor. This sensor is on the left front wheel, and is very similar to an ABS signal, this vehicle has no ABS, and has this single sensor, so I have changed it, and everything remains the same. I have several schemes of this vehicle, I do not know how to interpret them or I do not find it. Would anyone know how to guide me something? please?