Exploring Automotive Electrical Faults

What Are Some Simple Causes For Failing An Emissions Test?

Some states require scheduled emissions testing to be certain that vehicles conform to minimum pollution control requirements. In the event that a vehicle fails an emissions test, owners are usually required to have necessary repairs performed until the vehicle passes a subsequent retesting.

There are various reasons why a vehicle might fail an emissions test. Some issues are relatively simple and inexpensive to resolve, while others require specialized equipment in an auto repair facility.

Simple issues that may cause emissions test failure

Dirty air filter

Your vehicle has two air filters. The cabin air filter cleans the air that you breathe, while the engine air filter cleans the air that your vehicle needs for combustion. If the engine air filter is dirty and clogged, your vehicle needs to use more fuel to compensate for lack of oxygen. This results in lower gas mileage and exhaust that exceeds the standard requirements for passing the emissions test.

If your engine air filter hasn't been changed in the recent past, it's a good idea to replace it. Engine air filters are model specific, so be sure to get the correct filter. 

Older vehicles will often have a round ring filter, which can be replaced by removing the wing nut on the lid to the round filter compartment that sits atop the engine. Newer vehicles will have a rectangular cartridge filter, which can be replaced by moving the two metal clips that secure the lid on the rectangular shaped compartment beside the engine.

Dirty oil

If your oil hasn't been changed regularly, it has likely been transformed into a thick dirty sludge that can no longer perform its duties of protecting engine parts from wear and allowing the engine to perform at its optimal efficiency. 

Loose or ill fitting gas cap

A poorly fitting gas cap can allow vapors to be emitted that not only harm the environment but may also cause an emissions test failure. Fuel will also be lost due to evaporation and possibly contaminated from outside sources.

When replacing your gas cap, don't settle for a less expensive universal fit cap. Buy a cap for the specific year, manufacturer and model of your vehicle, because you want an exact fit that conforms to your vehicle. 

Leaking exhaust system

If your exhaust system has a hole or a loose clamp, the testing equipment at an emissions testing station may not be able to retrieve an adequate sample for testing.

Find a safe spot, and place a piece of cardboard or its equivalent under your vehicle. Take an adjustable wrench, gloves, and safety glasses with you and inspect the length of your exhaust system. Use the adjustable wrench to secure every bolted clamp along the line, and inspect for holes.

If a hole is found, you can use muffler repair cement or muffler repair tape to seal it, at least for sufficient duration to retake and pass a failed emissions test. While these quick fixes may temporarily solve the problem, a hole is usually indicative that the exhaust system is showing its age and will likely cause future problems until it is replaced.

Most of these simple repairs should be done whether or not they allow your vehicle to pass an emissions test. If simple solutions won't solve your emissions problem, you will need to turn it over to a professional. Sensors and other complex components will likely need to be diagnosed and repaired by an auto repair facility such as Pete's Service Center.