Your brake light being on will not cause a smog check failure, however taking the smog test with an empty gas tank might be an issue.
It is recommend to get a smog inspection with the fuel tank 1/4 to 3/4 full of gas. Low fuel in the gas tank might create low fuel pressure, leading to a lean fuel mixture, and ultimately resulting in possible high HC and high NOx.
posted by SmogTips Support
