I had the same problem with my 99 gsr when I got rid of the cat and put a test pipe in. Since mine was also obd2, I had 2 sensors. One in the front and one in the back. I extended the wire from the secondary sensor to the front of the test pipe where the other o2 sensor is located since the test pipe had 2 bungs right next to eachother. Now I still was getting the cel since the reading from the o2 sensor was not within spec. I resolved this by purchasing a obd1 p72 computer and the obd2-obd1 conversion harness. Now, no cel. I run a little rich, but at least my cel problem is solved.