2013 Mazda 6 - ECU/change odometer reading
 

So we recently replaced the ECU , cluster, keys the whole kit etc in our car with a used one. This however has now changed the odometer reading on our car to show the old cars odometer. Does anyone know how we can change this to reflect our cars correct mileage? Is this to be done on the cluster itself or the ECU? Hope this makes sense Thanks

Car mileage stored in the instrument cluster. Either reinstall the original cluster or take the car to a shop to correct the odometer, It's done thru OBD port.