SL 500 catalytic converter codes
Hi all, my 2003 SL500 has recently been throwing codes for the catalytic converter. Specifically I'm getting fault codes P207E-001 (P0432) and P200B-001 (P0422) using the STAR diagnostic system. The description reads "The efficiency of the left catalytic converter is insufficient" and the other one is the same but for the right side. The CEL pops on at random and sometimes goes away for a while, then comes back. The codes indicate a cat failure however I ALWAYS get both codes at the same time. In my opinion, the odds of both cats failing at exactly the same time is near zero, so I'm wondering if anyone knows what may be causing this or has dealt with this issue in the past? I'm stumped, and don't want to throw money at parts until I have a good sense that it will actually fix the problem.
As an aside, when I scan the car, the codes show up with a lower case "f" which I believe indicates a stored code rather than an active one. It seems like there is something that triggers this from time to time but not continuously.
Any leads or ideas would be greatly appreciated,
Thanks