1998 Chevy Cavalier ABS light

I changed the master cylinder on my 98 cav. Because the code said that the master cylinder was bad. I got one out a junk yard and put it in. The guy at the garage said that the code machine won't work because its a different master cylinder. He said it won't recognize the code because I changed it. He said the only way is to take it to a dealer to re program the computer. Is there another way? The abs light comes on when you start driving the car.