ThienNguyen

My ML320 got Chk Eng light turned on. I did use a diagnostic scan tool to retrieve code and found code P207E (Catalic converter redement too low (P0432) in register. I reset code, and occasionally re-run the diag and found the same code re-appeared but this time there's no check engine light . It might be because the error threshold has not reached to turn on the light ? There's some discussion about oxygen sensor . Can I get some expert opinion on this error code please ? Thanks for the help.