I bought my cat last summer. When I took it in for state inspection (TX) last summer they said I had a check engine light on. It wasn't the one on the dash but they said it was an interior light. I think they told me it was my maf sensor. I thought it was weird because I had no lights on inside the car and it passed emissions but they said when they plugged it in the computer a "check engine" code came up so they couldn't pass it. Has anyone heard of this other "check engine" light or has had the same problem?
Since the summer I have replaced the oil cooler (oil in resevoir), crank position sensor (engine stuttering), maf sensor, and spark plugs. Does the maf sensor affect gas mileage because it used to be horrible? I am on my first tank after installing the maf sensor so I'll keep you updated.
As far as I know, there is no interior CEL "light". However, there may be codes in the OBDC which are not currently illuminating the CEL. For example, a code might need to be present on three consecutive startups in order to illuminate the CEL. If your state requires no codes to be present, it will fail even with the CEL off.
I was lucky in VA. The CEL was off, but I have a permanent P0160 that I can't get rid of. Luckily, it still passed the inspection (I guess they don't check that one in VA).
The funny thing is since I bought the car I have never had a light on except when I forgot to connect some wires after installing my oil cooler. My car definetely doesn't stutter anymore and I think I'm getting better gas mileage. Hopefully it'll pass inspection this time. Thanks for the comments guys.