Toyota training course t852 engine control systems sec07

Technician Handbook
874 Engine Control Systems II

Evaporative
Emissions (EVAP)
System Overview

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.

EVAP Systems
Monitoring

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.

EVAP Systems

Technical Training

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)

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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
pressure being zero. Example: when the system takes a
reading of the atmospheric pressure (if applicable), it will set
Gauge pressure to zero, and pressures below this will be

displayed as negative values (-22 mmHg).

4.  Electrical valves may have to be checked several times and for
several seconds in order to diagnose an intermittent failure.
5.  To perform an active test, go to the Engine (and ECT) Live Tab
 Active Test  then choose the necessary active test. Once
the active test is entered, create a custom data list by selecting
the desired parameters (usually Vapor Pressure Abs and Vapor
Pressure Gauge) and clicking the New List button.

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874 Engine Control Systems II
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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Vapor Pressure
Sensor Overview

Though there are different styles of vapor pressure sensors, they use the
same style circuit.
The Vapor Pressure Sensor (VPS) measures the vapor pressure in the
evaporative emission control system. The vapor pressure sensor may be
located on the fuel tank, near the charcoal canister assembly or in a remote

location.
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
hose to atmospheric pressure. It is important that these hoses are
connected to the proper port. If they are reversed, DTCs will set.

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Prepare Vapor Pressure
Sensor for EVAP
System Diagnosis

In some instances, it may be necessary to disconnect hoses from the Vapor
Pressure Sensor (tank mounted VPS excluded) prior to test the EVAP
system for leaks. Be sure to follow Repair Manual or worksheet instructions
carefully when preparing the VPS for EVAP system testing. Also, ensure
that all hoses are reconnected to the VPS correctly after testing or repairing
the EVAP system.

Vapor Pressure Sensor

Diagnosis

Check all hoses for proper connection, restrictions, and leaks. Check the
VC and E2 voltages. Apply the specified pressure and read sensor voltage
output. The vapor pressure sensor is calibrated for the pressures found in
the EVAP system, so apply only the specified amount to prevent damaging
the sensor. Check the Freeze Frame data.

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874 Engine Control Systems II

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Early Type EVAP
System Overview

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 threeway 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
pressure.

Early Type EVAP
System Monitor

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
lines, charcoal canister, or fuel tank. A visual inspection of the EVAP
is performed for most EVAP diagnostic procedures. Inspection
begins with the filler cap, hoses, and tank.

Early Type EVAP
System Diagnosis Tips

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The procedure on the next page and the worksheet at the end of
this section are meant for training purposes only. When trying to
determine the cause of an Early Type 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).

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Technician Handbook
874 Engine Control Systems II

Early Type EVAP
System Diagnosis
NOTE

If multiple codes are displayed, diagnose them in the following
order: P0441, P0446, P0440.

P0440: Evaporative
Emission Control
System Malfunction

If DTC P0440 is present, the ECM detected atmospheric pressure in
the fuel tank side after the vehicle was idling for several minutes,
indicating a possible leak on the fuel tank side. Using the active test,
command the VSV for Vapor Pressure ON/TANK so tank pressure
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).

P0441: Evaporative
Emission Control

System Incorrect
Purge Flow

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.

Technical Training

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.

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P0441: Evaporative
Emission Control
System Incorrect
Purge Flow (cont’d)

P0446: Evaporative
Emission Control
System Vent Control
Malfunction

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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874 Engine Control Systems II

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Technician Handbook
874 Engine Control Systems II

Late Type EVAP
System Overview

The Late Type, also known as Intrusive Type, was developed to
meet the very stringent, mandated standard of detecting a 0.5mm
(0.020 inch) hole. This system uses many of the same components
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
at atmospheric pressure).
•  The three-way VSV has been replaced with a bypass VSV
which connects the canister and tank during monitor operation.
•  A closed canister valve (CCV) has been added on the air inlet
line allowing the system to be sealed.

Appendix A illustrates locations of the Late Type EVAP system
canister components.

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Vacuum in Tank/Relief
via Canister

Technical Training

Vacuum in the fuel tank can be relieved by allowing air to enter
through the canister. The CCV is normally OPEN, allowing fresh air
to enter the canister.

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Vacuum in Tank/Relief
via Tank Cap

130

Vacuum in the tank can also be relieved through the fuel tank cap.

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874 Engine Control Systems II

Pressure in Tank/Relief
via Canister

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Pressure in the tank can be relieved through the canister air drain valve.

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Purge

132

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

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Technician Handbook
874 Engine Control Systems II

ORVR Operation

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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.

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Late Type EVAP
System Monitor

A very small 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 Late Type 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.  After a period of driving (5–20 minutes) the ECM turns the purge
VSV ON.
3.  Next, the ECM will CLOSE the CCV (Canister Closed Valve) and
OPEN the bypass VSV while continuing to cycle the purge VSV.
This will lower the pressure in the EVAP system. If pressure does
not decrease, the ECM judges the purge system to be faulty and
sets DTC P0441: Purge VSV Operation.

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874 Engine Control Systems II
Late Type EVAP
System Monitor
(cont’d)

4.  When the pressure reaches a predetermined point, the purge
VSV is turned OFF and the ECM will measure the rate of

pressure increase in the system. 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 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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Late Type EVAP
System Diagnosis

When trying to determine the cause of a Late Type 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). The worksheet at the end of this
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.
Appendix A illustrates locations of the Late Type EVAP system
canister components.

NOTE

136

It is not recommended by Toyota to manually introduce vacuum with
a vacuum pump or shop air into any EVAP system as damage to
valves and components may occur. However, using engine vacuum
through the EVAP VSV with an EVAP VSV active test is OK as this
is how the ECM tests the system. When diagnosing the cause of
any EVAP system, use Toyota/Lexus approved SSTs such as the
EVAP Tester or Smoke Tester.

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LEV-II EVAP System
Overview

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.
•  The pipe diameter of the fresh air line and the flow rate of the
canister closed valve have been increased.
•  The ORVR (On-board Refueling Vapor Recovery) function has

been incorporated in the refueling valve.
•  A restrictor passage has been provided in the refueling valve to
prevent the large amount of vacuum during purge operation or
system monitoring operation from damaging the fuel tank.
•  The pressure switching valve has been discontinued.
•  An air filter has been added to the fresh air line. The air filter is
maintenance-free. If the filter becomes clogged, the ECM will set
DTC P0446.

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Technician Handbook
874 Engine Control Systems II

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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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
874 Engine Control Systems II

LEV-II EVAP System
Diagnosis

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.

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LEV-II with Vacuum
Pump (Key-OFF) EVAP
System Overview

The LEV-II with Vacuum Pump (Key-OFF) EVAP system was
designed to comply with CARB regulations. This new system began

to be phased in beginning in the 2004 model year. The LEV-II with
Vacuum Pump EVAP system is an enhanced version of the LEV-II
EVAP system. The malfunction detection method is similar to
previous systems in that vacuum is introduced into the system and
the internal pressure of the EVAP system is monitored in order to
detect leakage in the system. However, the readiness monitor runs
after the engine and ignition have been turned OFF, and vacuum is
provided by the vacuum pump incorporated into the newly adopted
pump module.
Listed below are the construction differences between this system
and the LEV-II EVAP system:
•  A pump module has been incorporated, which consists of the
canister vent valve, vacuum pump, vapor pressure sensor, and
a 0.020 inch reference orifice.
•  The vapor pressure sensor has been relocated to the pump
module and is non-atmospherically referenced (absolute
pressure is actual atmospheric pressure).
•  The canister vent valve has been incorporated into the pump
module.

NOTE

142

Later versions of the LEV-II with Vacuum Pump (Key-OFF) EVAP
system may not have a service port. The fresh air line is the most
effective entry point for diagnostic tools such as the EVAP System
Pressure Tester and EVAPro Smoke Tester.

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Technician Handbook
874 Engine Control Systems II

LEV-II with Vacuum
Pump (Key-OFF) EVAP
System Pump Module

Technical Training

The Key-OFF pump module contains the canister vent valve,
vacuum pump, pressure sensor, and 0.020 inch reference orifice.
The pump module is usually included with the canister assembly as
one part number. Refer to the vehicle Repair Manual for component
locations and details.

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