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Volkswagen Exhaust Pipe

Signs of Emission Control System Failure in Your Volkswagen

Post on July 28, 2019 by

Your Volkswagen’s evaporative emission control system, commonly referred to as an EVAP system, helps to reduce air pollution by restricting gases (evaporated and non-burned) from being released into our atmosphere. Examples of these common air-polluting gases produced by your VW are hydrocarbons, carbon monoxide, nitrogen oxide, and carbon dioxide.

There are symptoms to be aware of when this important system is failing in your vehicle. In this article, we have described what signs you should look for that may indicate an emission control system failure in your Volkswagen.

Understanding an Evaporative Emission Control System (EVAP)

The typical emission control system of a Volkswagen is comprised of the following important components:

  • Fuel Tank – stores gasoline/fuel as you fill the tank up
  • Fuel Tank Pressure/Fuel Rail Sensor – tracks the pressure of the fuel tank to detect leaks
  • Fuel Level Sensor – senses the amount of fuel in the gas tank
  • Gas Cap – seals the entire system from the atmosphere outside
  • Vapor-Liquid Separator – prevents liquified gasoline from seeping into the EVAP canister
  • Purge Valve – allows fuel vapors into the engine
  • Solenoid/Vent Control Valve – controls venting from inside the canister out into the atmosphere
  • Vent Hoses – allows fuel vapors to flow into the various areas of the system
  • EVAP Charcoal Canister – Cleans the fuel vapors prior to being released out into the atmosphere. It usually holds between 1-2 pounds of activated charcoal which has sponge-like properties due to its ability to absorb and store vapors as necessary.

Four Symptoms and Signs of Emission Control System Failure

1. Seeing the Check Engine Light Come On

Usually, the first sign of an EVAP problem is when the Check Engine Light (CEL) comes on. The performance of the canister purge valve is monitored and controlled by the car’s computer which will trigger the CEL to come one if it detects any abnormalities. It is important to pay attention to the light itself. If the CEL stays on indefinitely while you drive, and you do not detect any other performance issues, the emission control system has a permanent or long-term defect. If the CEL remains on with other performance problems, it reflects a more serious issue with one of the system’s vital components.

2. Noticing Lower Gas/Fuel Mileage

A canister purge valve that is not opening the right way will result in a partial loss of fuel that would otherwise be burned by your car. This loss will cause noticeably lower gas mileage in your vehicle.

3. Experiencing Rough Idling

A canister purge valve that is stuck open will create a vacuum leak. This leak changes the important air-to-fuel ratio and causes issues with your engine. One sign of this engine trouble is rough idling when your car is running as well as problems when starting the vehicle.

4. Smelling Strong Fuel Vapors

If the EVAP charcoal canister is damaged, cracked, or is leaking due to faulty seals of vents, you will be able to smell the odor of fuel vapors.

How an Emission Control System (EVAP) Can Fail

Your VW’s emission control system only works when certain sensors, chemical reactions, and vacuum controls operate properly. Normal age will cause a loss in the effectiveness of chemical reactions and cause decay and deterioration in rubber hoses, etc. Any of these can cause your system to stop working.

Other reasons why your emission control system may fail include:

  • Gas caps – loose, damaged, or missing (among the most common causes of system failure)
  • EVAP hoses – disconnected or leaking
  • Charcoal canister – leaking
  • Purge valve – damaged or faulty
  • Canister vent valve – damaged or faulty
  • Fuel tank – leaking

Help With Your Emission Control System

If your vehicle’s emission control system shows Volkswagen Emission Test any of these signs of possible failure, the Master Certified ASE technicians at Ultimate European Repair are here to help you diagnose the issue. Ultimate European Repair has served satisfied customers throughout the Goodyear, Buckeye, Avondale, Phoenix, and Peoria, AZ areas. As our name implies, we specialize in servicing a variety of European vehicle manufacturers and automakers, including BMW, MINI, VW, and Audi. Please contact us to set up an appointment so that we can begin helping you with all of your European vehicle needs.

Posted in Volkswagen Repair

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