I have a 99 GSR. I can't get my check engine light off. I did a diagnostic test and I keep getting a code 67. Code 67 is: catalyst system efficiency below threshold. I thought it ment it was stopped up. So i took it off and gutted it clean as a whistle and put it back on. I reset the computer and drove the car about a 100 miles. The check engine light came right on. I don't know if it is where the front o2 is reading the same as the rear o2 senser. Any advice would be appreciated. Thanks.