Top 7 Reasons for EVAP Fault Codes
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The Evaporative Emission System (EVAP) has been the cause of many check engine lights for years. From failed components to small leaks, the EVAP system can be difficult to diagnose. In the article, we will discuss the possible failures of the EVAP system and what you can do about it.
Before you start diagnosing the EVAP system in your vehicle, it’s important to understand the possible failures.
It is crucial to not replace parts based on fault codes alone.
For an overview of the EVAP system, check out this article.
Here are the top 7 reasons for EVAP fault codes:
Loose or worn gas cap
Over time, the gasket on the gas cap can become worn and not seal correctly. This can cause an EVAP leak. Check your gas cap and make sure it is tight.
EVAP purge valve
The EVAP purge valve is usually located near or on the engine. It is a mechanical device that allows fuel vapors to enter the intake system to be burned. Due to its mechanical nature, it can become stuck open or closed, or electrically fail.
EVAP vent valve
The EVAP vent valve is usually located underneath the vehicle. Just like the EVAP purge valve, it can also become stuck open or closed, or electrically fail.
Leak in a fuel vapor line
Leaks are the most common EVAP problems and can be difficult to pinpoint.
For more information about EVAP leaks and how to find them, check out this article.
Clog
Foreign objects such as dust, dirt, and bugs can enter the EVAP system and cause a restriction.
Faulty fuel tank pressure sensor
Measuring the pressure in the fuel tank is a key part of how the vehicle’s control module operates each component. Incorrect data from the fuel tank pressure sensor can cause misleading fault codes.
Software Update
In some cases, the vehicle’s control module may need a software update to enhance how the EVAP system is controlled.
Common fault codes of the EVAP system
P0440 - EVAP System Malfunction
P0441 - EVAP System Incorrect Purge Flow or Flow During Non-Purge
P0442 - EVAP System Small Leak Detected
P0443 - EVAP System Purge Control Valve Circuit or Incorrect Purge Control Valve Flow
P0445 - System Leak Detected
P0446 - EVAP Vent Solenoid Valve Control System
P0455 – EVAP System Gross Leak Detected
P0456 – EVAP System Very Small Leak Detected
P0457 – EVAP System Leak Detected (Fuel Cap) or EVAP Canister
How much can it cost to fix an EVAP issue?
The cost of fixing an EVAP issue depends on the severity of the problem.
If it is a component failure, it may be quick to fix and may have a low cost.
The cost of fixing an EVAP leak may be more costly because of the time spent to find the leak.
How does a mechanic diagnose an EVAP problem?
A professional mechanic diagnoses an EVAP problem by following these 6 steps.
Read the fault codes on a scan tool
Most scan tools will provide a fault code for the EVAP system.
Research the fault codes on an automotive information service, like Alldata or Identifix
Understanding the reason for the fault code is key to diagnosing the issue. A subscription to an automotive information service will provide fault code descriptions and wiring diagrams. Sometimes they will provide potential causes to fault codes.
Depending on the fault code, the mechanic will:
Test the EVAP components.
Hook up a smoke machine to locate a leak. Here is a link to Amazon to the smoke machine I use for every EVAP leak.
Find the problem
After testing, a component failure or EVAP leak will become evident.
Repair the problem
Retest to confirm the repair
The best mechanics will retest after the repair to confirm the problem is fixed.
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