Best card diagnostic solutions
  • Fast Dispatch And
  • Highest Quality
    Standard & Safety
  • 100% Satisfaction
  • Best Value for
    your money
  • Great Customer

Diagnostics and Repair: EVAP System

Diagnostics and Repair: EVAP System 1

Without keyword

EVAP system

Capturing excess fuel vapor from the vehicle’s fuel system

* EVAP system diagnostics

* Consider an EVAP system
Toyota cars as an example

* Some DTCs and their descriptions
for the initial type EVAP system

* Some DTCs and their descriptions
for the “subsequent” type EVAP system

* VPS sensor circuitry

* Curious case
diagnostic and repair system EVAP

In my opinion, this is one of the most not so complex, but very inconvenient systems for diagnosis. And this is confirmed by practice. Finding a small leak in the EVAP system is sometimes very difficult, especially without a good scanner that allows you to test the system in real time, as well as simply an indispensable smoke generator in this case, without which the leak search can become endless.

Usually, very few diagnosticians and services are taken to completely troubleshoot this system. The standard response in the auto service to a burning banner CHECK ENGINE and diagnostic codes DTC P0440 – P0457.

– Never mind!

They encountered this malfunction code, they know that the “code is complex”, but they respond in such a way as to “not penetrate and not create problems for themselves”:

– This code does not affect the speed, delete the error and drive yourself to your health!

Although in my practice there were quite serious injuries, delaying the elimination of which was fraught with serious troubles. For example, a car ignites when gas leaks through holes in a rotten gas tank on a fairly fresh 2004 Mitsubishi Outlender, or fuel leaks through leaks in the gasket of the gas pump assembly due to inaccurate installation after replacing the fuel filter. The gasket was forcibly bent and “out of place” crushed by a screwed cap on top.

Since diagnostics are my bread, and malfunctions in the EVAP system are quite common, I decided for myself to try to deal with this system, its “standard sores” and methods for eliminating them.

First, some history and statistics..

The first cars equipped with the EVAP system appeared in the state of California, USA, in the already very distant 1970.

Since 1996, after the entry into force of a new standard for monitoring OBDII vehicle systems, the EVAP system has been classified by 17 codes of possible malfunctions:

P0440. Evaporative Emission Control System Fault

P0441. Evaporative Emission Control System Incorrect Purge Flow

P0442. EVAP Emission Control System Leak Detected (small leak)

P0443. EVAP Emission Control System Purge Control Valve Circuit

P0444. EVAP Purge Control Valve Circuit Open

P0445. EVAP Purge Control Valve Circuit Shorted

P0446. Evaporative Emission Control System Vent Control Circuit

P0447. EVAP Emission Control System Vent Control Circuit Open

P0448. EVAP Emission Control System Vent Control Circuit Shorted

P0449. EVAP Emission Control System Vent Valve / Solenoid Circuit

P0450. Evaporative Emission Control System Pressure Sensor

P0451. EVAP Emission Control System Pressure Sensor

P0452. EVAP Emission Control System Pressure Sensor Low Input

P0453. EVAP Emission Control System Pressure Sensor High input

P0454. EVAP Emission Control System Pressure Sensor Intermittent

P0455. EVAP Emission Control System Leak Detected (gross leak)

P0456. EVAP Emission Control System Leak Detected (small leak)

P0457. EVAP Emission Control System Leak Detected (fuel cap)

Agree, a pretty impressive list, and if you take into account that according to American statistics, EVAP codes are the most common reason for car owners to call a car service, then it’s just not very reasonable to miss such a tidbit in your work.

Most common trouble codes

The following is a list of the most common trouble codes, and percentages is the percentage of car failures during tests in 2009 in America, Illinois:

P0420 – Catalyst System Low Efficiency – 13.2%

P0171 – Fuel Trim System Lean Bank 1 – 10.4%

P0401 – Exhaust Gas Recirculation (EGR) Flow Insufficient – 8.4%

P0174 – Fuel Trim System Lean Bank 2 – 6.8%

P0442 – Evaporative Emission (EVAP) System Small Leak Detected – 6.7%

P0300 – Engine Misfire Detected (random misfire) – 6.4%

P0455 – Evaporative Emission (EVAP) System Leak Detected (large) – 6.2%

P0440 – Evaporative Emission (EVAP) System – 5.5%

P0141 – Oxygen Sensor Heater (H02S) Performance Bank 1 Sensor 2 – 5.1%

P0430 – Catalyst System Low Efficiency Bank 2 – 3.2%

P0135 – Oxygen Sensor (HO2S) Performance Bank 1 Sensor 1 – 3.2%

P0446 – EVAP Vent Solenoid Valve Control System – 3.1%

P0128 – Coolant Thermostat – 3.1%

P0301 – Cylinder 1 Misfire Detected – 3.1%

P0411 – EVAP System Control Incorrect Purge Flow – 2.8%

P0133 – Oxygen Sensor Slow Response Bank 1 Sensor 1 – 2.8%

P0303 – Cylinder 3 Misfire Detected – 2.6%

P0304 – Cylinder 4 Misfire Detected – 2.6%

P0302 – Cylinder 2 Misfire Detected – 2.6%

P0325 – PCM Knock Sensor Circuit – 2.1%

P0420 leads by single codes , but if you break all the codes into systems,
then the picture is as follows:

Evaporative Emission System – 24.3%

Engine Misfire – 17.3%

Fuel Trim (lean) – 17.2%

Catalytic converter – 16.4%

Oxygen sensor related – 11.1%

Exhaust Gas Recirculation (EGR) system – 8.4%

I decided to see: “… what about us?” … and raised my notes for 9 months of 2011. The situation loomed a little different, problems in the EVAP system moved to second place, giving priority to problems with oxygen sensors, but still, 19% is a solid figure.

Oxygen sensor related – 29.6%

Evaporative Emission System – 19.0%

Engine Misfire – 18.6%

Catalytic converter – 16.6%

Fuel Trim (lean) – 9.6%

Exhaust Gas Recirculation (EGR) system – 6.6%

System diagnostics EVAP

Environmental regulations require the vehicle to be periodically monitored EVAP , determining its performance and tightness. This is all (and other components of the system), checked by measuring pressure at various stages of the system.

Some have suggested that connecting a smoke generator immediately is a panacea for solving all the problems in an EVAP system. I will not argue, I will answer this way: “Maybe …”, but personally I prefer to first localize the fault area with other available tools and only then, if necessary, connect the smoke generator. Moreover, not only discharge leaks can cause the recording of diagnostic codes, but also pollution of the system channels, failure of control valves and control sensors.

So, let’s move on to the diagnosis..

First step : “G seal system for testing .

This is usually achieved by plugging all the ventilation channels of the EVAP system manually or using a diagnostic scanner with the appropriate functions: you can select $ 08 – (control of on-board systems) in the diagnostic mode according to OBDII mode and force the system to be sealed for testing. If such a function is available, then there is no need to do anything extra, ECM will do everything for you. Then connect to the service port and create a discharge in the system. After the test, it is necessary to turn the ignition on and off so that the system goes into normal operation. If as a result of the test it was found that the system is not tight, then I initially check the fuel tank cap, seal it properly and repeat the test. If the vacuum drops anyway, then the lid has nothing to do with it and you can move on. Better check the system in parts

– line from intake manifold to canister

In the end, after localization and elimination of the leak, a final test of the entire system is carried out. Unfortunately, Check mode does not work for EVAP system codes and this slightly complicates the verification of completed troubleshooting.

But, for example, the Toyota TIS Techstream program has for almost all Toyota and Lexus models the Readiness Test Confirmation procedure utility with which you can check your work, – Fig. 1

Diagnostics and Repair: EVAP System 2

Or directly test the EVAP system in manual or automatic mode, but this is mainly for cars in the US market, – Fig. 2

Diagnostics and Repair: EVAP System 3

To diagnose the EVAP line from the canister to the intake manifold and to diagnose the canister itself, I usually use a vacuum pump, which is faster and more convenient. If a leak is detected, then I use a smoke generator to localize it and to check the fuel tank and filler neck. It is very important to consider the warning car manufacturers:

Do not use compressed air to test the EVAP system: a mixture of fresh air and fuel vapors is very dangerous and may result in fire or explosion..

Consider an EVAP system using an example Toyota cars

Initially, the cars used the Non-ECM controlled EVAP system – a system not controlled by an electronic control unit. The main components of this system were:

Fuel tank
Fuel cap with valve (vacuum check valve)
Charcoal canister
Thermo-Vacuum Cleaning Control Valve
Throttle EVAP port (typically, port P)

Diagnostics and Repair: EVAP System 4

After toughening environmental standards, a more advanced electronically controlled EVAP system has been introduced since the beginning of the 90s. This system is divided into two types. The first type is called “initial” or “spontaneous”, the second is called “subsequent” or “forced”. The ECM leak detection and monitoring algorithms for both types are different, as are the diagnostic procedures and DTCs .

The “original” type was designed to meet the initial EPA (Environmental Protection Agency) and CARB (California AirResources Board) leak detection requirements. This type of system can detect a leak with an existing hole of 1mm (0.040 in.) Or more. When leak detection standards became even more stringent, a “follow-up” type was introduced in 2000, in which the size of the hole leading to leakage, which should be monitored by monitoring, was halved to 0.5mm (0.020 in.).

The easiest way to determine what type of system is installed in the vehicle being diagnosed is to look at the ventilation duct of the EVAP system , which is attached to the air intake housing behind the air filter (if it is structurally provided). If the channel is connected directly, then it is a system of the “initial” type, if a solenoid called “the Canister Closed Valve” or abbreviated CCV is installed at the connection point , then this is a “follow-up” type system.

Another major difference between the two types is how the ECM detects system leaks. In both cases, the Vapor Pressure Sensor (or VPS) is used for this..

The “original” type system uses the 3-Way Vacuum Switching Valve (or VSV) to sequentially connect the Vapor Pressure Sensor (VPS) to two insulated parts of the EVAP system, from the canister side and the fuel tank side. When the 3-Way position is VSV – OFF, the part of the system is monitored from the intake manifold and the canister; when the position is ON, part of the system is monitored from the side of the fuel tank. This data is then compared with the reference data programmed into the ECM. The measured data is very small, in the region of 15.5 mmHg (0.3 psi) or less. If the received data exceeds certain limits, the corresponding DTC is written to the ECM and the CHECK ENGINE banner lights up on the dashboard .

Diagnostics and Repair: EVAP System 5

In the “follow-up” system, the VPS is connected to the fuel tank and does not connect to the canister, the 3-Way Vacuum Switching Valve is replaced by Bypass Vacuum Switching Valve , which combines two parts of the system for leakage testing, from the side of the fuel tank and from the side of the canister.

In contrast to the “initial” type system, during verification, the generated vacuum in the EVAP system is very small. Testing starts at the same time as starting a cold engine, when the readings of the coolant temperature and air temperature sensors are equal. The ECM constantly monitors the pressure in the fuel tank; as the fuel temperature rises, the pressure slowly and slightly rises.

To conduct a leak test, the ECM closes the CCV, opens the Bypass VSV, and opens the EVAP VSV purge valve which connects the entire system to the intake manifold to create the required vacuum test. Upon reaching a predetermined vacuum threshold, the ECM closes the EVAP VSV and monitors the rate of pressure drop in the system. If the data exceeds the expected values, the corresponding DTC is written to the ECM.

It should also be noted that the EVAP “2 trip codes” system malfunction codes and the CHECK ENGINE banner light up on the dashboard when the same malfunction is detected twice under the same test conditions during two car trips. System monitoring lasts 20-30 minutes or more to fulfill all necessary conditions. This accordingly complicates the quality control procedure of the repair work performed after the elimination of the malfunction..

And finally, if more than one fault code occurs in the EVAP system, it is advisable to start the system check by repairing the leak, and then diagnosing the component failure.

Some DTCs and Descriptions for EVAP “Initial” of type

P 0440 – EVAP System Malfunction .

This code occurs when the 3-Way VSV is turned on to check part of the system from the side of the fuel tank and the required vacuum is not created in the system, the pressure in the system does not differ from atmospheric pressure. A standard check by ECM may take more than 20 minutes.

With this code, first of all, it is necessary to check the fuel tank for leaks, the channel connecting the fuel tank and the canister, the filler neck and the gas tank cap – Fig. 6

Diagnostics and Repair: EVAP System 6

P 0441 – Vapor Purge Flow Detection

This is more complex code to fix. It can occur at two points in the EVAP system malfunction:

– there is no adequate flow of fuel vapor from the canister to the intake manifold (clogged channels, malfunction of the solenoid EVAP purge VSV)

– there is no tightness of the system from the canister to the intake manifold.

ECM sets this code under the following conditions :

1. If the discharge in the system, which should be created when opening EVAP purge VSV, does not reach the required level.

2. If the ECM determines that the vacuum in the EVEP system was created at the initial stage, when it should not occur, because the EVAP purge VSV should be closed.

3. If the ECM does not see rarefaction pulsations in the EVAP system at the moment when fuel vapor is transferred from the canister to the intake manifold.

If you only have this code, first of all you need to check the correct operation of the EVAP purge VSV and the system line from the canister to the intake manifold. But not only, because the ECM monitors this code based on the VPS, which in turn depends on the correct operation of the 3-Way VSV. Therefore, as practice shows, the code P0441 is almost always fixed along with the code P0446 we will consider it further.

P0446 – 3-Way VSV Fault (malfunction of a three-channel vacuum solenoid), – fig. 7

Initially, the ECM checks the operation of the 3-Way VSV by comparing the difference in pressure readings, alternately switching the solenoid and isolating the two parts of the system from the side of the fuel tank and from the canister. If there is no difference, then two options are possible:

1. If there are no vacuum fluctuations in the VPS readings corresponding to vacuum fluctuations in the intake manifold that are typical for normal engine operation when EVAP purge VSV is open , then the ECM assumes that the 3-Way VSV has not turned off (stuck in the on position). And / or …

2. If there are rarefaction pulsations in the system from the fuel tank side, then the ECM assumes that the 3-Way VSV has turned off and not turned on, or has jammed in the off position.

It is important to note that similar symptoms are also observed in the presence of leaks in the system as a whole, therefore it is quite natural that codes P0440 or P0441 will also be written to the ECM memory. If this is the case, before checking the 3-Way VSV, it is first better to check the entire system for the presence / absence of leaks and only after that deal with the valve itself. Canister internal malfunction is also possible..

If all possible reasons were checked and did not bring a positive result, as well as the “freeze frame” readings of the Freeze frame data indicate that the car was stationary at the time the code appeared (car speed 0 km / h), then the canister itself is quite likely to malfunction, – fig. 8

In fact, the 3-Way VSV malfunction is quite common, but placing the valve on the car creates certain difficulties for its diagnosis, and without a lift or inspection hole it is very inconvenient to diagnose it. Another factor complicating the diagnosis may be the lack of a good diagnostic scanner, with a slow flow of scanner data exchange with ECM it is quite difficult to see all the necessary information with VPS, in which case it is better to use an oscilloscope.

One way out of this situation:

* Using the appropriate wiring diagram, you can connect the oscilloscope to the VPS signal wire directly on the sensor connector or on the ECM connector (very often this is much easier to do there). Then activate the 3-Way VSV from the scanner and at the same time open the gas tank cover. Record the oscilloscope readings, they should correspond to atmospheric pressure. If such a result is obtained as a result of testing, then the system is not tight. Now close the fuel tank cap, turn off the 3-Way VSV, start the engine and activate the EVAP purge VSV, create a vacuum in the system, observing the changes in the oscilloscope reading. The system must contain rarefaction pulsations, which are also visible in the readings of the oscilloscope. After creating the necessary discharge, turn off the EVAP purge VSV, the ripple should stop and the signal should stabilize at a certain level. If the signal begins to change sharply, striving to the value obtained by us before the start of the test, then in the part of the system from the side of the canister there may be a leakage of the discharge, the reasons for which must be clarified and eliminated.

Some DTCs and Descriptions for the Next Type EVAP System

P0441 : Purge (EVAP) VSV Operation

At some point, the ECM closes the CCV and opens the purge (EVAP) of the VSV and bypass VSV creating a vacuum throughout the EVAP system until it drops to the set value. Then the purge (EVAP) VSV closes and the vacuum readings are compared with the reference. If the vacuum is not created or it goes beyond the limits set by the program, then the ECM will fix the fault (EVAP) of the VSV and its associated components. It should be borne in mind that if there are vacuum leaks in the system, the symptoms of the malfunction will be very similar, and if the malfunction code is not one but several, for example also P0440 or P0442, then it is more rational to check the system for leaks first, and then go directly to diagnose purge (EVAP) VSV. In the active tests of many scanners, there is a forced open / close function purge (EVAP) VSV function – this greatly simplifies the verification procedure.

P0440 & P0442 : HC Leak Detection (from 2000 to 2002)

The pressure boost rate recorded by the VPS indicates whether there are leaks in the system and what type of leaks. Leaks are divided into two types: Gross leak (Small leak), Small leak (small leak) and are classified as follows:

When the threshold pressure level is reached in the system, the ECM closes the purge (EVAP) of the VSV and monitors the rate of decrease in discharge. A sharp drop in vacuum refers to a large leak and is fixed by code P0440. A small drop in vacuum is the norm, if this threshold is exceeded, then this is attributed to a small leak and the code P0442 is written..

P0446 – Vent Control-Canister Closed Valve & Bypass Valve Operation

At this stage, the correct operation of the two control valves and the condition of the ventilation channel of the EVAP system from the canister are monitored. At the start of the test, the system must be sealed. Validation logic has nothing to do with the previous system and the earlier version of P0446.

Upon reaching the set threshold of discharge, the ECM closes the purge (EVAP) of the VSV, opens the CCV and monitors the rate of decrease of the discharge, if the speed is insufficient or the discharge does not decrease at all, then this is treated as a CCV malfunction or a dirty ventilation duct (an example of the reason for such a code will be given below).

The second part of the test is as follows: with the CCV open, the ECM closes the Bypass Valve, isolating the fuel tank from the rest of the system. If at this moment the pressure drop in the fuel tank does not stop, the ECM determines the Bypass Valve malfunction. It is better to start troubleshooting with CCV, it is very simple: you need to check its electrical part, functionality and tightness. Troubleshooting the Bypass Valve is also easy. After checking its electromechanical part, very similar symptoms of malfunction are present and in the presence of leaks in the system, therefore, usually P0446 is accompanied by codes P0440 & P0442.

If more than one code is written to the ECM, it is best to first identify leaks, and then proceed to check the control valves.

P0442, P0455 & P0456 : HC Leak Detection (since 2003)

After the next tightening of environmental requirements, leaks are once again further divided into three types: Gross leak (large leak), Small leak (small leak), Very small leak (very small leak). The classification criteria are as follows:

P0442 (EVAP 0.04 inch leak – a small leak)

* when the system reaches a predetermined vacuum threshold from -20 mmHg (-2.67 kPa) to -17 mmHg (-2.27 kPa), the vacuum sharply decreases over the next 5 seconds by more than 1.3 mmHg (0.17 kPa).

P0456 (EVAP 0.02 inch leak – a very small leak)

* when the system reaches a predetermined vacuum threshold from -20 mmHg (-2.67 kPa) to -17 mmHg (-2.27 kPa), the vacuum decreases over the next 5 seconds by more than 0.7 mmHg (0.09 kPa).

P0455 (EVAP gross leak)

* upon opening the purge (EVAP) VSV, the discharge in the system for a certain period of time does not reach the set value by more than 1.3 mmHg (0.17 kPa).

P0450 or P0451 – Vapor Pressure Sensor Fault

Both of these codes are directly related to the EVAP pressure sensor. The verification algorithms and conditions for the occurrence of codes are identical for the “initial” and “subsequent” types of systems. They are recorded in the memory when the signal from the sensor goes beyond the permissible limits programmed in the ECM.

Verification of the P0450 code is as follows:

* after starting the engine, the ECM monitors the voltage on the VPS signal wire for 10 seconds, and if the voltage for 7 seconds out of 10 exceeds 4.5v or less than 0.5v, then the sensor is considered faulty.

Code P0451 will be written if, after the first 10 seconds of engine operation, VPS readings go beyond 4.9v and 0.1v for at least 7 seconds, and also if between 5th and 15th seconds after stopping operation engine VPS readings fluctuate beyond the limits of the programmed characteristics. For example, if at least 7 oscillations are detected in 10 seconds (from the 5th to 15th second) exceeding 3.83V (+5 mmHg) and 2.77V (-5 mmHg), then the VPS sensor will be recognized by the ECM as faulty.

Principle of operation of the VPS sensor

VPS sensors are of two types and can be located on different cars in different ways: on the canister, on the fuel tank or separately. In accordance with the location, there are structural differences. For example, a sensor located on a fuel tank does not require a supply of vacuum tubes, but they are necessary for other types of sensors. There are one and two channel options. The sensitivity of the sensors used is very high, they are able to monitor changes 1.0 psi = 51.7 mmHg.

To check, you can use both a scanner and an oscilloscope. The check consists of the usual procedures: checking the availability of power and good ground, the integrity of the wiring from the ECM to the VPS, the absence of corrosion and the presence of good contacts directly in the sensor connector. Of course, you must also verify the integrity of the vacuum channels connecting the VPS to the system. When checking the operability of the sensor, it is impossible to create a vacuum more than acceptable in the EVAP system, otherwise it will lead to the sensor failure (for a “subsequent” type system, this is more than -20 mmHg). Freeze frame data can also be very useful, if the DTC is recorded less than 200 seconds after the engine starts, then this is a good hint that the VPS itself is faulty.

Wiring diagram for VPS sensor. Fig. thirteen

This is a brief overview of the EVAP system, the main problems and how to solve them. And in conclusion, I want to introduce you to the story of our American colleague. What are the “abnormal” malfunctions of the EVAP system, quite interesting.

A Curious Case for Diagnosing and Repairing an EVAP System

Northampton, Pennsylvania, USA

Read materials available only to registered users

P0446 EVAP Vent Performance & Spiders!

(insufficient ventilation performance of the EVAP system and spiders)

In the original, the decoding of this code P0446 – EVAP Vent Solenoid Valve Control System, sounds like this – “problems in the solenoid control system controlling the EVAP ventilation”.

The essence of the note is as follows: “… the cause of the above code was the nest that the spiders made in the solenoid (EVAP Vent Solenoid Valve) and the eggs laid by them almost completely blocked the access of fresh air through the ventilation duct to the storage absorber”.

The method by which Andrew Satko determined the likely area of ​​malfunction is quite simple and will certainly be of interest to novice diagnostic technicians. He, using a scanner, forced the EVAP PSV to open on the 20th century, created a pressure of -10mmHg in the system, then closed the EVAP PSV, he opened the EVAP VSV and watched the pressure drop in the system, which quite smoothly and slowly dropped to 0 mmHg. Then he did the same procedure, but instead of opening the EVAP VSV, he slightly opened the gas tank cap, the pressure rose sharply to 0 mmHg in a matter of seconds. Based on this, he suggested that the ventilation duct is partially clogged, which confirmed the further actions, analysis and analysis of the EVAP VSV and ventilation duct.

After the forced eviction of the spider family, the system worked fine and the burning CHECK ENGINE banner on the dashboard no longer bothered car owners.

I wrote a lot, but I hope that my practical research in this area will help my colleagues. The article used personal best practices and materials of the open foreign press.


  • Diagnostics and Repair: EVAP System 7

    Toyota EVAP Evolution

    Without keyword As the theory teaches, about 20% of the hydrocarbon (CH) emissions from cars come from the evaporation of fuel. The system for trapping…

  • Diagnostics and Repair: EVAP System 8

    Diagnostics and repair – what are the benefits of TSB

    Without keyword What is a TSB? This is the “Technical Service Bulletin “, a special document issued by the Manufacturer to “catch up” with those cars…

  • Diagnostics and Repair: EVAP System 9

    EGR system repair

    Without keyword How “some” diagnosticians work in “some” car services: they see the code or codes of malfunctions on the scanner display, erase them,…

  • Diagnostics and Repair: EVAP System 10

    Diagnostics of malfunctions of an air conditioning system

    Diagnostics of malfunctions of an air conditioning system COOLING PROBLEM? The most common cause of problems with the cooling system is the lack of…

About admin

Leave a Reply

Your email address will not be published. Required fields are marked *

© Copyright 2018 Carscanners. All rights reserved.

Enjoy this blog? Please spread the word :)