Toyota training course t852 engine control systems sec07

874 Engine Control Systems II Technician Handbook The EVAP system’s purpose is to reduce the amount of fuel vapors that the fuel tank and fuel system release into the atmosphere.. 874 E

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874 Engine Control Systems II

Technician Handbook

The EVAP system’s purpose is to reduce the amount of fuel vapors that the fuel tank and fuel system release into the atmosphere Usually the customer is unaware of an EVAP system issue until the MIL illuminates, as EVAP problems typically do not create driveability concerns The customer needs to be aware that they must correctly install the fuel cap after refueling

A common EVAP failure is a leak in the system, but restrictions and other failures will also set EVAP related DTCs

Regulations require that the EVAP system be monitored for system performance and leak detection Leaks, restrictions, and many components are checked by measuring the pressure of the EVAP system through the Vapor Pressure sensor

at various stages of the monitor

Early EVAP systems had to detect a 1mm (0.040 inch) hole and greater

The system that complies with this regulation is known as the Early Type

or Non-Intrusive

Beginning with the 2000 model year, regulations required that EVAP systems had

to detect a 5mm (0.020 inch) hole and greater This regulation also required vapor purge and component performance to be monitored The first system that met this regulation was the Late Type or Intrusive

All EVAP system DTCs are two trip

There are a variety of EVAP systems in use with different monitoring strategies It

is essential that the EVAP system be correctly identified before beginning diagnosis The best source for identifying the EVAP system on a specific vehicle is the Repair Manual Below is a list of the most common types of EVAP systems:

•  Early Type (Non-Intrusive)

•  Late Type (Intrusive)

•  LEV II

•  LEV II with Vacuum Pump (Key-OFF)

•  Closed Fuel Tank (hybrid vehicles)

Evaporative Emissions (EVAP)

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Technician Handbook

EVAP Diagnosis Tips 1.  It is essential that the EVAP system be correctly identified before

beginning diagnosis The best source for identifying the EVAP system on a specific vehicle is the Repair Manual

2.  Set TIS Techstream Vapor Pressure units to mmHg Go to Setup

 User Preferences  Unit Selection  Vapor Pressure:

mmHg This is to match Repair Manual specifications

3.  Some systems will display Vapor Pressure in two different ways:

Absolute and Gauge

•  Absolute is the pressure reading based on an atmospheric scale Example: when the system is exposed to atmospheric pressure and the vehicle is at sea level, the Vapor Pressure will be approximately 762 mmHg

To use this reading, it is necessary to record the atmospheric pressure when the system is exposed to atmospheric pressure before beginning diagnosis

•  Gauge is the pressure reading based on the atmospheric

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Technician Handbook

EVAP Diagnosis Tips

(cont’d)

6.  A System Check can be performed on some EVAP systems To

perform an EVAP System Check, go to Engine (and ECT) Live Tab  Utilities  EVAP System Check

7.  As fuel temperature increases it will increase the pressure in the fuel tank This is why some rise in EVAP system pressure is expected when the system has been exposed to vacuum

8.  The EVAP System Pressure Tester (Essential Tool SST No

00002-6872A) can be used to diagnose the source of an EVAP system leak Always check the EVAP System Pressure Tester for internal leaks by following the procedure on the inside of the tool’s case lid Ask your instructor to demonstrate the use of this tool

9.  The approved smoke tester (Approved Dealer Equipment Catalog Model No ETI2000E) is very effective for diagnosing EVAP system leaks Always follow the directions supplied with this tester The fresh air line is the most effective entry point for the smoke tester; however, VSVs may have to be commanded with active tests to allow the smoke to enter the entire EVAP system Ask your instructor to demonstrate the use and effectiveness of this tool To order this tool, call the Approved Dealer Equipment Catalog phone number at 800-368-6787

10. The EVAP adapter SST number 00002-6872A-ADP3 attaches to the fresh air line at the canister

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This sensor uses a silicon chip with a calibrated reference pressure on one side of the chip The other side of the chip is exposed to vapor pressure

Changes in vapor pressure cause the chip to flex and vary the voltage signal to the ECM The voltage signal out depends on the difference between atmospheric pressure and vapor pressure As vapor pressure increases, the voltage signal increases This sensor is sensitive to very small pressure changes (1.0 psi = 51.7 mmHg)

Vapor Pressure Sensors come in a variety of configurations When the VPS

is mounted directly on the fuel pump assembly, no hoses are required For remote locations, there may be one or two hoses connected to the VPS If the VPS uses one hose, the hose is connected to vapor pressure In the two hose configuration, one hose is connected to vapor pressure, the other

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Technician Handbook

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Technician Handbook

The ECM relies on the vapor pressure (VP) sensor signal to accurately measure pressure in the EVAP system and the purge side of the charcoal canister The changes in the pressures being measured are very small, often 15.5 mmHg (0.3 psi) or less For the

VP sensor to measure tank pressure and canister pressure, a way VSV is connected to the VP sensor, fuel tank and lines, and charcoal canister When there is no power to the three-way VSV VP sensor, the VP sensor measures canister purge pressure When the ECM turns the VSV ON, the VP sensor measures fuel tank

three-pressure

The ECM tests for leaks by measuring EVAP system pressure in the lines, charcoal canister, and fuel tank When the EVAP pressure is higher or lower than atmospheric pressure, the ECM concludes that

no leaks are present EVAP pressure is measured by the VP sensor

If either the tank or canister purge side is at atmospheric pressure under specific conditions, the ECM determines there is a leak The leak could be a filler cap not properly tightened, or a hole in the

Early Type EVAP

System Overview

Early Type EVAP

System Monitor

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can be monitored and observe the Vapor Pressure parameter If the

fuel tank pressure is at atmospheric pressure, there may be a leak

on the fuel tank side Inspect the fuel cap and fuel tank side for a leak (brown in the illustration)

If P0441 is present, the ECM detected vacuum at the charcoal canister when the system was not purging, or a positive pressure at the canister during purge

1.  Verify the EVAP purge VSV does not leak when OFF With the engine running, disconnect the electrical connector at the purge VSV Remove the line between the purge VSV and canister Place a finger over the exposed purge valve nipple If vacuum is felt, replace the purge VSV If vacuum is not felt, proceed to step 2

Early Type EVAP

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Technician Handbook

2.  Using the active test, turn the purge VSV ON and verify

proper duty cycling while monitoring Vapor Pressure (at the

canister) Verify that pressure at the canister is well below atmospheric pressure (if atmospheric pressure is 762 mmHg, pressure at the canister during this step should be around 744 mmHg) If pressure does not change when the purge VSV is switched from OFF to ON, check the purge VSV for an inoperative condition, possible electrical malfunction, or a stuck open condition from a foreign object Also, check that the lines to the purge VSV are installed correctly

If P0446 is present, the ECM detected atmospheric pressure at the canister after the purge cycle completed, or the pressure of the canister and fuel tank remained the same indicating a problem with the VSV for vapor pressure control (three-way VSV)

1.  Using the active test, turn the purge VSV ON and monitor the

Vapor Pressure parameter If the pressure does not drop, the

purge VSV may be malfunctioning or the VSV for vapor pressure may be malfunctioning (looking at the tank side pressure only)

2.  If the pressure does drop, turn the purge VSV OFF and watch the canister pressure The pressure should rise slowly, taking approximately one minute for the pressure to rise back to atmospheric

3.  If the pressure rises rapidly, turn the purge VSV ON and use pinch-off pliers to pinpoint the leak on the canister side of the system (yellow in the illustration)

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Technician Handbook

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as the Early Type Purge, vacuum relief, pressure relief, and ORVR operations are identical to the Early Type However, the following items have been changed:

•  The VP sensor is connected to the tank and is not switched to the canister It is atmospherically referenced (set to 762 mmHg

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Technician Handbook

Purge During purge, vapors are drawn out of the canister and burned in

the engine

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Technician Handbook

ORVR stands for On-board Refueling Vapor Recovery During refueling, the differential pressure valve and air drain valve are open Fuel vapors are absorbed by the charcoal canister and excess air is vented to the atmosphere

ORVR Operation

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Typical enabling conditions necessary for this system’s monitor to run include:

•  MIL OFF

•  Fuel tank is approximately ½ to ¾ full

•  Altitude 7,870 feet (2,400 meters) or less

•  ECT and IAT between 40 and 95 degrees F (4.4 and 35 degrees C)

•  ECT and IAT within 13 degrees F (7 degrees C) of each other The following is a general overview of the Late Type EVAP system monitor operation:

1.  The monitor sequence begins with a cold engine start The IAT

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Depending on the size of the leak, the ECM will set either DTC P0440 or DTC P0442: EVAP System Leak Detected As

a general rule, a rise of 2 mmHg per 5 seconds is acceptable

5.  Next, the ECM will OPEN the CCV and monitor the vapor pressure sensor for a fast rise in pressure If the rise in pressure is not sharp enough, the ECM will set DTC P0446:

Vent Control, CCV Operation and Bypass VSV Operation

6.  Finally, the ECM will OPEN the purge VSV and end the test

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section and SB EG005-01 (Toyota) represent approved diagnostic

methods

For model year 1996–2003 vehicles, the LEV-II EVAP system monitor drive pattern can be accessed in the RM section of TIS2,

found in a document entitled “OBD II: General Information.” The

readiness monitor drive patterns are in the General  General Information  OBD Monitor Drive Patterns section of this document

A manual EVAP System Check can be performed with the

Techstream to aid in diagnosis of this EVAP system To perform an

EVAP System Check, go to Engine (and ECT) Live Tab  Utilities

 EVAP System Check

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Technician Handbook

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Technician Handbook

The LEV-II EVAP system was designed to comply with new regulations issued by CARB This EVAP system began to be phased in beginning with the 2003 model year The LEV-II EVAP system construction has been simplified, resulting in improved reliability and serviceability This system consists primarily of a canister closed valve, purge valve, charcoal canister, vapor pressure sensor, refueling valve, and ECM

The malfunction detection method is similar to the previous EVAP systems Vacuum, provided by the engine, is introduced into the system, and the internal pressure of the fuel tank is monitored in order

to detect any leakage in the system

Listed below are the construction differences between this system and the Late Type EVAP system:

•  The air drain valve has been discontinued The air that has been cleaned through the charcoal canister is discharged through the fresh air line

•  The fresh air inlet has been moved from the air cleaner to a location near the fuel inlet

LEV-II EVAP System

Overview

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Technician Handbook

LEV-II EVAP System Monitor

Vacuum is applied to the EVAP system The ECM determines if there is a problem in the system based on the vapor pressure sensor signal

Typical enabling conditions necessary for this system’s monitor to run include:

•  MIL OFF

•  Fuel tank is approximately ½ to ¾ full

•  Altitude 7,870 feet (2,400 meters) or less

•  ECT and IAT between 40 and 95 degrees F (4.4 and 35 degrees C)

•  ECT and IAT within 13 degrees F (7 degrees C) of each other

The following is a general overview of the LEV-II EVAP system monitor operation:

1.  The monitor sequence begins with a cold engine start The IAT and ECT sensors must have approximately the same

temperature reading and be between 50 and 90 degrees F

2.  Once all enabling conditions have been met, the ECM commands both the purge VSV (VSV for EVAP) and the CCV valves OPEN If the system develops high negative pressure, the ECM determines that the CCV is stuck CLOSED and sets DTC P0446

3.  Next, the ECM will CLOSE the purge VSV and the CCV If the system develops high negative pressure, the ECM determines that the purge VSV is stuck OPEN and will set DTC P0441

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Technician Handbook

LEV-II EVAP System Monitor

(cont’d)

4.  Next, the ECM will OPEN the purge VSV If pressure does not decrease, the ECM determines that the purge VSV is stuck CLOSED and sets DTC P0441

5.  When the pressure reaches a predetermined level, the ECM will CLOSE the purge VSV and will measure the amount of pressure increase The rate of pressure increase indicates if there is a leak and if it is large or small Depending on the size of the leak, the ECM will set the following DTCs:

•  If the ECM determines there is a very small leak in the system, it will set DTC P0456

•  If the ECM determines there is a small or medium leak in the system, it will set DTC P0442

•  If the ECM determines there is a large leak in the system, it will set DTCs P0441, P0442, and P0455

6.  If the ECM determines there is no leak in the system, it will command the CCV OPEN and watch for a sharp rise in pressure

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Technician Handbook

When trying to determine the cause of a LEV-II EVAP system issue, check the Freeze Frame data and duplicate the conditions Use the Technical Information System (TIS) for Repair Manual (RM) and Electrical Wiring Diagram (EWD) information, and look for applicable Service Bulletins (SB)

For model year 1996–2003 vehicles, the LEV II EVAP system monitor drive pattern can be accessed in the RM section of TIS2,

found in a document entitled “OBD II: General Information.” The

readiness monitor drive patterns are in the General  General Information  OBD Monitor Drive Patterns section of this document

For model year 2004 and later, the LEV II EVAP system monitor

drive pattern can be accessed from the Readiness Monitor Drive Pattern section of the vehicle Repair Manual

A manual EVAP System Check can be performed with the TIS

Techstream to aid in diagnosis of this EVAP system To perform an

EVAP System Check, go to Engine (and ECT) Live Tab  Utilities

 EVAP System Check

For training purposes, the system leak diagnostic procedure for the LEV-II w/ Vacuum Pump (Key-OFF) EVAP system can be used to diagnose LEV-II EVAP system leaks; however, the engine must be running to provide the vacuum source

LEV-II EVAP System

Diagnosis

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