Defective fuel tank vent valve: symptoms and causes

If the fuel tank vent valve is defective, this can lead to a number of symptoms indicating a problem with the venting of the tank.

Symptoms of a defective fuel tank vent valve

A defective tank vent valve can manifest itself in a number of ways. You should take these signs seriously to avoid possible damage:

• Difficulties when refueling: If the fuel tank vent valve is defective, excess pressure can build up in the tank. This makes refueling more difficult and the fuel only flows slowly or intermittently into the tank.
• Odor after refueling: Another typical symptom is a strong smell of gasoline, especially after refueling. If the fuel vent valve is defective, fuel vapors may be released uncontrollably, causing unpleasant odors near the vehicle.
• Engine performance issues: A faulty EVAP can cause what is known as a ‘tank vacuum’, which affects the air supply to the engine. This can cause erratic engine performance, bucking or even an unexplained engine stall.
• Dashboard warning light: Many modern vehicles are equipped with on-board diagnostics (OBD) that can detect faults in the vehicle. A faulty EVAP valve will often cause a warning light to illuminate on the dashboard, often in the form of a “check engine” lamp.
• Higher fuel consumption: A defective tank vent valve can also cause fuel consumption to increase. The problem arises from the poor venting of the tank and an insufficient supply of the required air to the engine.

Causes of a defective tank vent valve

A defective tank vent valve can have various causes. In most cases, it is wear or improper handling.

• The EVAP valve is usually connected to a small hose that is in contact with the ambient air. Over time, dirt, debris or condensation can cause blockages that prevent the valve from functioning properly.
• In some cases, the EVAP valve is not checked during regular vehicle maintenance, which can lead to a defect. An undetected defect can persist for a long time and lead to serious symptoms.
• Extreme temperatures can damage the EV’s EVAP valve. Excessive heat, such as from frequent summer driving or frequent refueling of very hot fuel tanks, can wear out the valve. Similarly, freezing temperatures in the winter can jam the mechanism or damage the valve’s seals.
• Another common reason for a defect is rust or corrosion, especially in older vehicles or in vehicles that are often driven in areas where a lot of salt is used on the roads. Corrosion damage to the components of the fuel tank vent valve can cause it to malfunction.
• The EVAP valve is designed with seals to prevent the escape of gases. Over time, if these seals become porous or damaged, the valve will not close properly, resulting in a leaking vent.