Failed emission test despite no CEL.

[BeetleBuzz]

I took my parents' New Beetle (previously owned by me) for yet another emission test with full confidence of passing it. No issues with the car at all, no CEL, CEL light functional, etc. To my surprise it failed, and the cause was 3 old engine error codes stored in the memory. I don't recall the exact info for them but 2 were misfires, and one was an sec. air inj. pump incorrect flow detected b.s.

Is anyone aware of the logic they use to determine if a car passes or fails? In my understanding, if no CEL, no problem. Who cares if there are old engine codes in the memory, if there's no problem reported at the present moment that means there's no problem. Am I right?

[Smileybug]

CEL is usually a good indicator, but I would think they could base it off of codes. There are plenty of codes that will get stored but not throw a CEL. I've had the code throw for my temp sensor but it didn't trigger the CEL. I had one for the O2 sensor dying that didn't trigger the CEL until the thing finally completely died.

Best advice is when you fix things on your car due to codes, clear them out. Also if you have access to a VAG-COM, scan the car periodically for those codes that might not trigger the light. I usually scan mine every 6 months or so. You can sometimes figure out problems before they throw the light.