If you haven't had a smog check done recently, then you may be surprised that you no longer need a tailpipe emission test. Federal laws require that in areas where a smog check is required, most cars built after 2000 only need on-board diagnostic (OBD II) test. If your car was built between 1996 and 1999, then you will still get the standard tailpipe emissions test in addition to your OBD II test. However, although your car doesn't require a tailpipe emissions test, it can still fail, even if it's running perfectly. Here are a few reasons why your car may fail this type of test.
Your check engine light is on:
This would be a failure even if with the old smog check system as it indicates that something is wrong with your emissions components. The computer senses these things wrong and triggers a readable code which tells you what component has failed. If your check engine light is on, have your vehicle repaired before you go to your smog check.
"Monitor readiness" has failed:
This is a common, yet troublesome, problem many people have when going through their smog check. You may not know that you have a monitor readiness failure until the tests are performed. Basically, your vehicle performs a number of tests every time you start and drive your car. If you've recently disconnected the battery, or had a problem related to your check engine light repaired recently, then it's possible your car has not been driven long enough to complete all its checks. One solution is to not get a smog check right after having your car repaired. Drive the car around for a few days before your test.
System problems and tampered components:
If your car's computer system has problems, then you may get a failure because it won't communicate properly with the smog test computer. Also, if your car's emission components have been tampered, removed or replaced with improper parts, then you could also fail the tests. One thing many people miss is that those devices which monitor your driving habits, such as for your job or insurance company, should be removed before the test as they are considered an automatic fail if they're found still plugged in.
Smog testing for newer cars has changed and you may not be required to do a tailpipe emissions test. However, that does not mean it will be any easier for your car to pass if it has problems. Make sure you repair any problems related to the check engine light, and drive your car around for a few days before getting tested. If you have any questions about this type of test, talk to your smog technician about anything you may need to do to prepare.