The CEL does come on. I had the car tested and the scan code was P0420. sys eff below threshold (bank 1). .5 needs SOP CAT That is what the Toyota dealer gave me. So, I took it to a Lexus dealer and they said it was only a gas cap. Natually I replaced the cap as opposed the converter.It still comes on periodically. Actually there are 2 lights that come on. One says "V"SC the other “VSD OFF”.