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Common Symptoms Of The Faulty Evaporative (EVAP) Emission Control System

Published on December 26th, 2023

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Purpose

To discuss the five common symptoms that occur when the Evaporative Emission Control (EVAP) System fails.

Introduction

The EVAP system is part of a vehicle's emissions control system that prevents the release of fuel vapors into the atmosphere. It captures and stores fuel vapors from the fuel tank and fuel system, which are then burned off as part of the combustion process. This system is designed to be a closed system, sealed to prevent fuel vapors from escaping. It is made up of various components, including the fuel tank, fuel filler neck, purge valve, charcoal canister, hoses and lines. The system is monitored by the vehicle's On-Board Diagnostic System, which triggers a Malfunction Indicator Light (MIL) to alert the driver of any issues. Proper maintenance and inspection of the system can help ensure it is working correctly and reducing harmful emissions.

There are some symptoms to determine a malfunction in the EVAP system. These are:

  • MIL ON
  • Fuel Odor
  • Decreased Fuel Economy
  • Hard Starting or Rough Idle
  • Failed Emissions Test
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Symtoms of faulty EVAP Emission Control System

Symptoms of a faulty Evaporative Emission Control System

MIL ON

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When an issue occurs with the EVAP system, the vehicle's Onb-Board Diagnostic System will detect the problem and illuminate the MIL on the dashboard. The specific Diagnostic Trouble Code (DTC) stored will depend on the nature of the failure, and a professional mechanic can use a Scan Tool to retrieve the code and diagnose the problem.

Fuel Odor

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Fuel odor is a distinctive smell of gasoline or diesel fuel that is often associated with a leak in a vehicle's fuel system. It can occur when fuel vapors escape from the fuel tank, fuel lines, or fuel injectors and enter the passenger compartment of the vehicle or are released into the atmosphere.

A strong smell of gasoline around the vehicle can be an indication of an EVAP system failure. An EVAP system failure can cause decreased fuel efficiency, engine performance issues, and damage to the environment. A mechanic can inspect the system for leaks and replace any damaged components to resolve the issue.

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Hard Starting or Rough Idle

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When the EVAP system is not functioning properly, it can cause the engine to start hard or run rough. The reason behind this issue is often a malfunctioning Purge Valve that regulates the flow of fuel vapors to the engine. If the Purge Valve is stuck open or closed, it can cause the engine to run poorly or not start at all. A defective Purge Valve can also manifest itself through symptoms like reduced engine power, sluggish acceleration, and even engine stalling.

Decreased Fuel Economy

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The EVAP system plays a crucial role in reducing harmful emissions from the vehicle, which can also affect the vehicle's fuel economy. When the EVAP system is not working correctly, it can cause the engine to run less efficiently, which can lead to reduced fuel economy over time. This can result in higher fuel costs for the vehicle owner. Other symptoms of reduced fuel economy may include a decrease in engine power, poor accelera

Failed Emissions Test

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If the EVAP system is not functioning properly, it can result in higher emissions from the vehicle, which can cause the vehicle to fail an emissions test. Other symptoms of a failed emissions test may include increased emissions, poor acceleration, or decreased overall vehicle performance.

Summary

The EVAP system is responsible for regulating fuel vapors and preventing them from escaping into the atmosphere. When it fails, it can cause many problems in the vehicle's fuel system and emissions control. If you notice any of these symptoms, it's essential to get your vehicle checked by a qualified mechanic to diagnose and fix the issue. An EVAP system failure can cause several problems that can increase emissions and affect your vehicle's safety, and performance.

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