4 ms·

For a programmer, the answer should be "always", because smog check in the US is just self reported car diagnostics.

• function_seven 8y ago
  Varies by state. In California, we put the car up on a dynonometer and run it through various speeds and engine RPMs, while measuring the tailpipe emissions. Gas cap is checked to ensure good seal, and the MIL (Check Engine light) is tested to make sure it both works, and is off.
• oliveshell 8y ago
  ...except in California, to which the parent comment is clearly referring; there, emissions testing equipment is attached to your vehicle and particulate output measured.
• gtdawg 8y ago
  The other responses to this post may be thinking of CA vehicles year 1999 and older which require tailpipe measurements and dyno loading. Newer vehicles usually only require the OBDII review and they will double check codes haven't been cleared recently and all sensors are in spec. No dyno or tailpipe measurements are required in CA on year 2000 and newer. This is why smog shops offer $20-$40 for year 2000 and newer and $70+ for 1999 and older. It's more human time intensive to test year 1999 and older.
  • 1996 8y ago
    Pre OBDII now qualifies as antiques, which I think are emission exempt in most states. Post OBDII, codes not recently cleared is also reported by OBDII. It is just software, and the software can pretend what the programmer wants. So I maintain my answer: always