1997 Honda Accord CHECK ENGINE LIGHT ON

I have a 97 Honda Accord with a mileage of 112,000. For the past month, I had trouble with the catalytic converter and the distributor. I changed the catalytic sensor as well as the distributor. These 2 problems occurred simultaneously. Now, my check engine light is on and when I took in the shop, it shows Efficient low gas Sensor Bank #1 (something like that). So the mechanic just turned it off for me hoping that this was just because the sensor hasn't recognized the changes we made but I came back a week after because the light turned on again and its the same diagnostic from the computer. What can be wrong with this? Thanks!