Main Reasons Why Cars Don’t Pass Emissions Testing

Emissions tests are required to make sure that the levels of noxious gases, including nitrogen oxide, particulate matter, carbon monoxide, formaldehyde and non-methane organic gases emitted by the cars on the road do not exceed the legal limits. During the testing, the car’s tailpipe emissions are measured with various devices and the vehicles that have emissions exceeding the limits are not allowed to use the road until the necessary repairs are done to pass the test. In some cases, the remedy is quick and easy, while in other cases, it can be costlier and lengthier – here some of the most common reasons why cars receive failed emissions test:
  • Old and clogged spark plugs – these small and inexpensive components are essential for maintaining fuel emission levels low, their fault being among the most common causes of failed tests;
  • A damaged catalytic converter – this component is responsible for converting toxic gases into non-toxic gases, so if the converter fails, the car will fail the test;
  • Dirty air filters – the air filter is another inexpensive part that is essential for healthy emissions levels;
  • Damaged exhaust pipe – if your exhaust pipe is broken or punctured, your car will probably fail the emissions test. Fortunately, exhaust pipes are easy to test and to repair.