Will a failing camshaft sensor cause car to fail smog

Hello, any diagnostic trouble codes that are set due to an engine performance problem will prevent your vehicle from passing a smog test. So, in theory, yes -- a failing camshaft sensor would cause a trouble code and that would cause a failed smog test. On the other hand, a code related to camshaft position as read by the sensor is not necessarily an indication of a failing sensor. You'll need to troubleshoot the cause of any present code to determine the source of failure, and then make repairs to resolve the concern.