Imagine driving down the highway, then suddenly your check engine lights flash. Then a Diagnostic Trouble Code P0442, P0455, or P0456 is shown on scanning your DTC Computer. Gosh! One thing is for sure, there is a leak in your Evaporative Emission System (EVAP) and you have no choice but have to deal with the EVAP system leak repair cost.
It just doesn’t seem fair that this system, this thing that your car doesn’t even need to run, should cause so much aggravation.
The EVAP system is a closed system in your vehicle. It captures vapors from the fuel tank and keeps them from leaking out into the atmosphere. This makes the vehicle more environmentally friendly to operate.
If the check engine light comes on because of a problem or specific failure within that system, it’s very unlikely you’ll notice any difference in the actual operation of the vehicle. That’s because the EVAP system doesn’t affect your driving, it only affects your emissions.
There are a variety of potential causes for EVAP system issues, including leaks, a missing or loose fuel cap, an incorrect type of fuel cap used on the vehicle or leaks in the fuel tank, evaporative emission canister, evaporative emission system hose, purge valve or vent valve.
In this article we discuss:
What Is An EVAP System?
The Evaporative Emission Control (EVAP) System seals the fuel system of the vehicle to prevent fuel vapors (gasoline) from the fuel tank and fuel system from escaping into the atmosphere.
This is important because fuel vapors contain a variety of hydrocarbons. Hydrocarbons form smog when they react with air and sunlight.
Gasoline evaporates quickly, so if the fuel system is open to the atmosphere, a vehicle can pollute 24 hours per day without even being turned on. These uncontrolled evaporative emissions account for as much as 20% of the pollution produced by a vehicle.
The EVAP system usually requires no maintenance, but faults can turn on the check engine light and prevent a vehicle from passing an OBD II plug-in emissions test.
OBD 2 EVAP
The OBD II EVAP monitor on 1996 and newer vehicles run diagnostic self-checks to detect fuel vapor leaks, and if it finds any (including a loose or missing gas cap), it will set a fault code and turn on the check engine light. However, the EVAP monitor only runs under certain operating conditions. This may create a problem for the vehicle owner if his vehicle must be given an OBD II plug-in emissions test, and the monitor has not completed.
Common problems with the EVAP system include faults with the purge valve that vents fuel vapors to the engine, leaks in the vent and vacuum hoses, and loose, ill-fitting, or missing gas caps. The most common fault code is P0440, which shows a large leak (often a loose gas cap). EVAP Purge valve codes P0443 to P0449 are also common.
The code you don’t want to see is a P0442. This shows the system has detected a SMALL leak, but small leaks can often be a BIG problem to find. By small, we mean a leak no larger than a pinprick! Such small leaks are virtually impossible to find visually, so a special tester called a smoke machine is usually necessary to reveal the leak.
The smoke machine feeds a mineral-oil-based vapor into the EVAP system under light pressure (only a few pounds per square inch). The smoke may also contain an ultraviolet dye to make it easier to see under UV light.
Fixing EVAP codes can be a challenge, even for professional technicians. And if you have a P0442 small leak code, you will probably have to take your car to a repair shop that has a smoke machine and deal with EVAP system leak repair cost.
What Are The Components Of An EVAP System?
The Evaporative Emission Control System EVAP system comprises the following components:
#1. Fuel Tank
The fuel tank stores the gasoline when you fill it up. But, you know when people tell you not to continue filling the tank after the pump automatically stops? That is because the tank has some expansion space at the top so the fuel can expand without overflowing or forcing the EVAP system to leak.
#2. Gas Cap
Tighten until it clicks. The gas cap seals off the filler neck of the gas tank from the outside atmosphere. Damaged or missing gas caps are the most common cause of EVAP system leak codes that trigger the check engine light.
#3. Liquid-Vapor Separator
This prevents liquid gasoline from entering the EVAP canister, which would overload its ability to store fuel vapors.
#4. EVAP Canister
This canister is connected to the fuel tank by the tank vent line. The EVAP canister houses 1 to 2 pounds of activated charcoal that acts like a sponge by absorbing and storing fuel vapors until the purge valve opens and allows the vacuum of the engine intake to siphon the fuel vapors from the charcoal into the engine intake manifold.
#5. Vent Control Valve
This allows the flow of the fuel vapors from the fuel tank into the EVAP canister.
#6. Purge Valve/Sensor
Allows engine intake vacuum to siphon the precise amount of fuel vapors from the EVAP canister into the engine intake manifold.
#7. Vent Hoses
The means by which the fuel vapors flow to different components of the EVAP system.
#8. Fuel Tank Pressure Sensor
Monitors the pressure within the fuel tank for leaks and to make sure too much pressure does not build.
#9. Fuel Level Sensor
Monitors the level of fuel in the tank.
Which Are The Available EVAP Systems?
There are different evaporative emissions control systems. These systems can be classified into five different categories:
- Diurnal: This usually represents gasoline that evaporates because of the rise in ambient temperature.
- Running losses: Represent gasoline that vaporizes because of the heat of the engine and exhaust system during normal operation.
- Resting losses: Natural permeation that occurs from the fuel delivery system while not operating under ambient conditions.
- Hot Soak: Vaporization of fuel because of the keep heat of the engine after the engine is turned off.
- Refueling: Represents the fuel vapors that escape from the tank by the displacement of liquid fuel.
Why Is An EVAP System Necessary In A Car?
The EPA requires EVAP systems on cars because gasoline fuel vapors contain a variety of different hydrocarbons (HC). The lighter elements in gasoline evaporate easily, especially in warm weather. These include aldehydes, aromatics, olefins, and higher paraffins. These substances react with air and sunlight (called a photochemical reaction) to form smog.
Aldehydes are often called instant smog because they can form smog without undergoing photochemical changes.
The bad thing about fuel vapors is that fuel evaporates any time there is fuel in the tank. That means if the fuel system is unsealed or open to the atmosphere, it can pollute 24 hours a day even if the vehicle is not being driven.
Uncontrolled evaporative emissions like this can account for as much as 20 percent of the pollution produced by a motor vehicle.
The EVAP system eliminates fuel vapors as a source of air pollution by sealing off the fuel system from the atmosphere. Vent lines from the fuel tank and carburetor bowl route vapors to the EVAP storage canister, where they are trapped and stored until the engine is started.
When the engine is warm and the vehicle is going down the road, the PCM then opens a purge valve, allowing the vapors to be siphoned from the storage canister into the intake manifold. The fuel vapors are then burned in the engine.
Evaporative emission controls were first required on cars sold in California in 1970. EVAP has been used on all cars and light trucks since the early 1970s.
How Does The EVAP System Work?
The evaporative emission control (EVAP) system captures gasoline fumes and other emissions.
When the fuel evaporates inside the gas tank, the excess vapors are transferred to the charcoal canister. They’re stored there until they can safely be transferred back to the engine to be burned with the normal air-fuel mixture.
When that’s ready to happen, a valve creates a vacuum that draws the vapors into the engine. Fresh air is also drawn in through the vents and valves to mix with the vapors for better combustion. These systems can be controlled mechanically, or like on newer cars, through the engine’s computer.
If the fuel tank was sealed tight, the fuel pump could create enough negative pressure to collapse it.
So, on older EVAP systems, the tank is vented by a spring-loaded valve inside the gas cap. While, On newer vehicles, it is vented through the EVAP canister.
It’s difficult to wrap your head around how a typical EVAP system works. But the good news is that the system’s functions can be broken down into three primary operations: storing fuel vapors, purging fuel vapors, and self-monitoring.
The EVAP system has three primary operations:
- Storing fuel vapors.
- Purging fuel vapors.
#1. Storing Fuel Vapors
The vapor canister is the focal point of the EVAP system. When the engine is off, fuel vapors from the gas tank are stored in the canister. The canister contains activated charcoal, which traps the vapors until the engine is running, and conditions are correct for a vapor purge.
Normally, the vapor canister is open to the atmosphere to allow fresh air to enter. The canister is only closed when the EVAP monitor is run.
#2. Purging Fuel Vapors
In modern vehicles, the PCM determines when to start a canister purge. When the module deems conditions to be correct, it commands a solenoid to open the purge valve.
Opening the purge valve creates a vacuum that pulls fresh air through the vapor canister. The fresh air picks up the fuel vapors and delivers them to the engine to be burned during the normal combustion process.
#3. Monitoring For Leaks And Proper System Operation
As was mentioned, all vehicles built after 1999 have enhanced EVAP systems that can perform self-tests for both leaks and proper system operation. This test sequence is referred to as the EVAP monitor.
The monitoring strategy will vary, depending on the type of vehicle. When the conditions are correct, the control module closes the vent valve and opens the purge valve, creating a vacuum in the system.
The control module then monitors the fuel tank pressure (FTP) sensor to verify the system can reach a specified amount of vacuum.
If the vacuum is lower than specified, the module assumes there is a large leak somewhere in the system and stores a DTC in its memory.
What Is An EVAP System Leak?
An EVAP system leak is a leak somewhere in the EVAP system. If the size of the leak exceeds a certain value, the PCM will notice it while running the EVAP monitor. When this happens, the module turns on the check engine light and stores a DTC in its memory.
A professional technician (or skilled DIYer) can retrieve these codes with a scan tool or code reader.
Sometimes, an EVAP system leak may also trigger the check gas cap warning (on vehicles so equipped). When this happens, you have an EVAP system repair cost awaiting to keep your car environmentally friendly.
The EVAP monitor tests the system for both small and large leaks. Examples of DTCs that correspond to leaks include:
- P0442 Evaporative Emission System Leak Detected (small leak)
- P0455 Evaporative Emission System Leak Detected (gross leak/no flow)
- P0456 Evaporative Emission System Leak Detected (tiny leak)
A loose gas cap causes an EVAP system leak code. If your car has a leak code stored, try tightening the gas cap. If that doesn’t do the trick, you might swap out the gas cap, since replacements are relatively inexpensive.
Pinpointing an EVAP leak that’s not the gas cap can be difficult. Usually, the process requires the use of a professional smoke machine, which forces smoke into the EVAP system so that (hopefully) the leak will become visible when smoke billows out.
What Are The Symptoms Of An EVAP System Leak?
Potential signs of an EVAP system leak can unfold in different ways. And when you see any of these signs, then prepare for an EVAP system leak repair cost to fix the leak immediately. These symptoms include;
#1. Poor Gas Mileage
A low gas mileage shows that your vehicle is not operating at optimum efficiency. It also signifies that there is a high consumption or leakage of gas in your vehicle’s system. Several factors can make your vehicle have low gas mileage, including a lousy EVAP system. Here, this happens because the fuel vapors your vehicle usually uses during combustion get burned up to the environment before getting to the combustion chamber.
This means that you will lose some amount of your gas usually used during combustion, which causes your vehicle to have low gas mileage, increasing your budget by buying gas for the vehicle. This can get your vapor canister saturated or clogged.
#2. Poor Engine Performance
An EVAP system leak is bound to cause poor engine performance. Your engine will have a less effective operation, producing not enough power for any acceleration. This might cause your vehicle to have a sluggish movement, even as you apply pressure on your gas pedal.
An incomplete combustion process generated because of an EVAP system leak will cause your vehicle to have a sluggish acceleration, which you have to address immediately to prevent any undesirable condition.
#3. Difficulty In Starting Up The Engine
Difficult starting is also amongst the symptoms showing your vehicle has an EVAP system leak. This is because of a vacuum leak developed from issues with your charcoal canister, and it might make your vehicle’s engine difficult to kick off.
When you have a vacuum leak, it will permit unmetered air into your engine, which can unbalance the mixture of the air-fuel ratio, which will develop issues in your engine’s system by disturbing the internal combustion process. If this fault is left to continue, it can eventually lead to your vehicle not starting.
An unbalanced air-fuel ratio during combustion can lead to improper combustion because of an exorbitant amount of air in the engine.
#4. Engine Check Light Turns ON
Your engine check light will come ON when you have an EVAP system leak. If your vehicle’s computer system detects a fault within your EVAP system, it will illuminate the engine check light to tell the driver that there is an issue with the engine system.
The computer system picks up this fault via signals from your EVAP system. However, the engine check light can turn ON because of several other problems, so it’s advisable to properly scan your vehicle for error codes with an OTC Leak Tamer or use another smoke machine to get the actual fault responsible for turning the engine check light ON.
#5. Rough Idling
A prevalent symptom of an EVAP system leak is when your vehicle has a rough idle. The vehicle cannot maintain a high speed because of an unstable rpm count, or you might feel a shaking sensation in your vehicle while driving. Usually, your vehicle should have a stable rpm rate of about 1000.
If this rpm is fluctuating, you are looking at an idling issue. Rough idling can be because of faulty spark plugs, carburetor problems, dirty fuel injectors, and a vacuum leak.
A vacuum leak can occur because of a damaged or faulty EVAP system or hoses. When you notice this symptom, you need to immediately attend to it, as it can severely damage your engine system.
#6. Gasoline Odor
Gasoline odor is amongst an EVAP system leak symptoms and can result from various faults or engine problems in your vehicle’s system, but one of the major causes is a broken EVAP canister. A damaged vapor canister can give out a strong gasoline smell when it is bad.
#7. Failed Emission Test
Your vehicle will fail emission testing if you have an EVAP system leak in your system because of the emission of gas fumes. This type of fault will also illuminate the engine check light.
How Is An EVAP System Leak Detected And Fixed?
Finding leaks in the EVAP system can be very difficult. It often requires using a special “smoke machine” that generates a fine mineral oil mist that is pumped into the EVAP system under very light pressure. The mist circulates through the plumbing and eventually seeps out through the leak, making the leak visible. The mist may also contain ultraviolet dye to make any leaks more visible when illuminated with a UV lamp.
Below is a step-by-step fix to an EVAP System Leak Repair cost:
Verify that the gas cap is firmly tightened onto the gas tank entry point. The EVAP system also monitors the gas tank, so an open gas cap can be the primary source and perhaps the only leak in the system. Leave the fuel filler door open after you tighten the cap.
Kick a pair of chocks behind the rear wheels and lift the front end of the vehicle with a floor jack far enough that you can fit underneath. Secure it on a pair of jack stands.
Locate the EVAP service port adapter within the engine’s compartment. Typically, the port is near the engine’s front on the passenger side. You’ll see a valve and supply hose protruding outward.
Place the smoke machine tester’s hose into the service port adapter. Turn on the smoke machine by choosing the “Test” mode.
Allow the smoke to fill the EVAP system for approximately 60 seconds and dim the lights in your work area. Complete darkness would be preferred, if not for the obvious danger of hitting your face in a car.
Visually inspect the EVAP system by running the UV light across the vehicle’s underside, following the system’s path from the engine compartment to the rear fuel tank. Any smoke leaking from the system will illuminate in ultraviolet light.
Check the fuel cap; cap seal failures are very common in older vehicles. Replace any leaking or cracked hose within the EVAP system. In addition, repair or replace any EVAP purge valve that may emit fumes.
Can You Drive Despite An EVAP System Leak?
The answer is, yes, it’s usually safe to continue driving. But because the leak increases the amount of pollution the vehicle emits, fix the problem as soon as possible.
EVAP systems can also suffer from problems other than leaks. There’s a wide range of DTCs devoted to everything from a blocked vent valve to inadequate purge flow.
What Is EVAP System Leak Repair Cost?
EVAP system repair cost can be between $100 to $600. The cost of repair depends on two factors: the leakage location and the cause of leakage. However, other causes require a minor repair to fix, which will not cost so much.
But if the repair requires the replacement of various components in your EVAP system, it can build up to a high repair cost. Your vehicle’s model is also a determining factor of how high your repair cost will amount to.
Reliability: EVAP System Leak Repair Cost
The biggest benefit of getting the EVAP system repaired or replaced is that you will experience better gas mileage. Saving money on fuel and going further on a single tank is an advantage. You’ll also produce emissions at a reduced rate. You can pass an emissions test if one is required, only after you have had the new EVAP system put in.
Final Thought: EVAP System Leak Repair Cost
First, the (EVAP) emission control system; prevents the escape of fuel vapors from a vehicle’s fuel system. So, when the engine is running, a purge valve opens, allowing the vacuum to siphon the fuel vapors into the engine.
In addition, fixing (EVAP) codes can be a challenge, even for professional technicians. In addition, if you have a P0442 small leak code, you’ll probably have to use a smoke machine to find it and this might increase your EVAP system leak repair cost.
These tools have been tried and tested by our team, they are ideal for fixing your car at home.