Quote:
Originally Posted by khail19
A lot of things can cause a car not to pass smog, could be as simple as needing a tune-up or as expensive as an engine re-build.
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This. It has to pass a visual inspection, having all of the original smog equipment in place and operating properly, and well as a 2-speed tailpipe test, and a visual smoke test (can't be smoking out of the tailpipe or the engine compartment). As far as the tailpipe "sniffer" test, it's not just testing for unburnt fuel. HC (hydrocarbons, or unburnt fuel) can fail you, but so can CO (carbon monoxide) and NOx (oxides of nitrogen).