Reasons Cars Fail an Emission Test

Before you think of getting a new vehicle, it is advisable to consult with your state laws on emission tests. This is because most countries require annual emissions tests before you can be allowed to drive. You can’t get on the road minus a clean bill of health for your vehicle.

During these examinations, most cars and trucks are also required to pass an emissions test. If the vehicle fails, it will not receive a valid inspection sticker. In most cases, the problem must be repaired, and the vehicle must be re-inspected within a month.  Let’s have a look at the five common reasons for failed car emission test;

Faulty EVAP System

car emission testThe Evaporative Emission Control System in your automobile is responsible for preventing the release of toxic exhaust fumes into the atmosphere. If there is a leak in the vacuum hoses or vents, a defective purge valve, or even a loose or cracked gas cap, the system will not perform its primary function. Repairing these problems is generally inexpensive since affected components are easy to access.

A Damaged 02 Sensor

When the oxygen sensor in your automobile goes bad, it will not be able to measure the amount of oxygen in the exhaust gas accurately. This can increase the toxicity of the fumes that are expelled from your tailpipe, which almost always results in a failed inspection. In addition to possibly increasing the toxicity of exhaust gas, a faulty 02 sensor can reduce engine power and fuel efficiency. In extreme cases, it may also cause your engine to overheat. Replacing the part generally costs between two and three hundred dollars at your local auto repair shop.

Exhaust Outflow

A leak in your car’s exhaust system can cause all sorts of problems, from reduced fuel efficiency and increased engine noise to pedal vibrations and much dirtier gas fumes. Because the problem throws off the readings of the 02 sensors, even a small leak can result in a failed inspection. Repair costs for the problem can range from under one hundred to several hundred dollars. Rich

Fuel Mixture

test for emission on a carAlso known as running rich, high amounts of carbon monoxide in your car’s exhaust fumes means that its engine is burning too much gasoline. There are numerous explanations for a rich fuel mixture, including leaky fuel injectors, a bad oxygen sensor, excessive pressure, or a faulty mass airflow sensor. Anyone of them will likely set you back a few hundred dollars. Wrong Fuel


Several automotive components work together to ensure that the proper amount of gasoline is being burned at all times. If there is a problem with the fuel injection unit, the carburetor, or the engine control unit, metering may be adversely affected, causing more gas to be burnt than is needed. As you might expect, a vehicle that is using more gasoline than required will not pass the emissions test. These problems can cost several hundred dollars to repair.

If you fail your next emissions test, there’s an excellent chance that one of these problems is to blame.