My CEL keeps coming on for secondary O2 sensor. If my car is burning too lean could that cause it to trip the sensor? The sensor has been goes off randomly ever since I did the swap. I put an HKS cat-back exhaust the same time as the swap. I had my stock cat so I swapped it out with a High flow cat that isn't suppose the trip the O2 sensor. Later the CEL came on again so I changed the sensor and it came on again. The car is burning very lean. Any suggestions?