Reasons Your Car Might Fail an Emissions Test

Reasons Your Car Might Fail an Emissions Test

A failed emissions test can put your car out of commission, and leave you without a way to get where you need to be until the issue causing the failure is fixed. While most vehicles are capable of easily passing emissions tests with flying colors, it’s still important to understand what can cause an emissions test failure and why.

Here are two reasons why your car could fail an emissions test.

#1: Check Engine Light is on

The engine of your car is a remarkable machine that depends on dozens of parts and systems to work together to function as intended. When the check engine light comes on, then it’s a guarantee that your car will fail an emissions test. While there are a number of varying reasons that can cause your check engine light to come on, some of the most common reasons that directly relate to emissions include a faulty oxygen sensor and damaged catalytic converter.

  • Faulty oxygen (02) sensor: When a gasoline-powered engine burns gasoline there is oxygen present. And the oxygen 02 sensor is designed to monitor what’s happening with the fuel mixture. Over time, contaminants may accumulate on the sensor which reduces the sensor’s ability to regulate the oxygen and fuel mixture. A faulty sensor can increase the output of emissions and eventually lead to a damaged catalytic convertor.
  • Damaged catalytic converter: Your catalytic converter has an extremely important job—take the emissions produced by your engine and chemically convert toxic gasses that are harmful to public health into less-toxic ones. Without a catalytic converter, your vehicle would put out far more emissions than it does. A leaky or faulty catalytic converter will cause you to fail emissions tests almost immediately since they’ll allow a lot of unfiltered emissions to escape. This is perhaps the most frustrating reason to fail an emissions test because replacing a catalytic converter is expensive—these small devices use precious metals like platinum as a part of the exhaust conversion process, so buying a new one can be extremely costly.

# 2: Leaking Gas Cap

This might be possibly the easiest emissions failure problem to fix. A leaking gas cap can make it impossible to recover the emissions that come from fuel evaporating in your fuel tank. This evaporation is perfectly natural, but sucks the fuel out of your tank and prevents you from being able to use that fuel to drive. But thanks to your EVAP system, evaporated fuel vapors can’t escape your vehicle, and instead you can use them to power your car when you restart it.

Your gas cap is part of the EVAP system. A faulty or leaking gas cap which isn’t absorbing vapors will lead to a dry EVAP system, which usually notifies your car computer that something is wrong and causes you to fail emissions tests. What you may not realize is that your check engine light that turns on may simply be because your gas cap is loose or developed a leak. A new gas cap generally costs just a few dollars from your local auto parts store, and takes just a minute or so to replace.

If your vehicle has failed an emissions test, book a service appointment with your local Christian Brothers Automotive!

Each shop is locally owned and operated providing full service auto repairs for all make and models. Search our interactive map here to find a location near you.

Posted by, Christian Brothers Automotive