EVAP System: Description

While the engine is running, if predetermined conditions (closed loop, etc.) are met, the purge VSV is opened by the ECM (included in the hybrid vehicle control ECU) and stored fuel vapors in the canister are purged to the intake manifold. The ECM will change the duty cycle ratio of the Purge VSV to control purge flow volume.

Purge flow volume is also determined by the intake manifold pressure. Atmospheric pressure is allowed to enter the canister through the vent valve to ensure that purge flow is maintained when negative pressure (vacuum) is applied to the canister.

The ECM monitors the condition of both the key-off monitor and purge flow monitor to ensure proper operation of the EVAP system.

Components	Operation
Canister	Contains activated charcoal to absorb fuel vapors that are created in fuel tank.
Cut-off valve	Located in the fuel tank. Valve closes by its own weight when vehicle is overturned to prevent fuel from spilling out.
Purge VSV	Opens or closes line between canister and intake manifold. ECM (included in the hybrid vehicle control ECU) opens and closes purge VSV to control EVAP purge flow. ECM opens purge valve to purge the fuel vapors that were absorbed by canister to intake manifold. ECM controls EVAP volume purged to intake manifold by duty cycle (current-carrying time) to purge valve. (ON: Open, OFF: Closed)
Roll-over valve	Located in fuel tank. Valve floats and closes when fuel tank is filled to 100%. Also, valve closes by its own weight when vehicle is overturned to prevent fuel from spilling out.
Soak timer	Built into ECM (included in the hybrid vehicle control ECU). To ensure that EVAP monitor values will be accurate, soak timer counts 5 hours (-15 minutes) from when power switch is turned off. This will allow fuel to cool down, which will stabilize Fuel Tank Pressure (FTP). When approximately 5 hours have passed, ECM turns ON (refer to Fig 5).
Fuel vapor-containment valve	Opens and closes line between fuel tank and canister. When vehicle is stopped, this valve stays closed to keep fuel vapors in the tank and prevent them from being absorbed by canister. During refueling, valve opens to allow fuel vapors from tank to be absorbed by canister. When the vehicle is being driven, the valve maintains a slight positive pressure in the fuel tank.
Fuel tank pressure sensor	Converts pressure in fuel tank into voltage reading for use by ECM (included in the hybrid vehicle control ECU). ECU supplies 5 V to sensor, and uses voltage reading that is output as feedback to allow monitoring of fuel tank pressure (refer to Fig 5).
Canister pump module	The following 5 items labeled (a) to (e) are canister pump module components. Canister pump module cannot be disassembled.
(a) Vent valve	Can either close vent for canister, or open vent to atmosphere. When ECM (included in hybrid vehicle control ECU) turns valve on, canister vent is closed. Alternately, when ECM turns valve off, canister vent is opened to atmosphere. To check for leaks in EVAP system, purge VSV is left closed, vent valve is turned on (canister vent is closed), and vacuum pump is operated to create a vacuum (negative pressure) is system (refer to Fig 3).
(b) Canister pressure sensor	ECM (included in hybrid vehicle control ECU) applies 5 V to pressure sensor, allowing it to create voltage reading that is used by ECM to detect pressure in canister (refer to Fig 4).
(c) Check valve	Composed of nylon ball and spring. Valve blocks off atmosphere from outlet of vacuum pump.
(d) Leak detection pump	Used to create negative pressure in EVAP system to allow checking for leaks.
(e) Reference orifice	The diameter of reference orifice is 0.02 inches. Vacuum (negative pressure) is created, and pressure is measured with purge VSV closed (off) and vent valve off (in vent position). This reference pressure is used to set a baseline (criterion pressure) against which a small leak can be judged.

Key-off monitor 

This monitoring system checks for canister pump module malfunctions and leaks from the EVAP and closed tank systems. Be sure to leave the vehicle for at least 5 hours to sufficiently cool the fuel and stabilize fuel tank pressure. This makes EVAP system monitoring more accurate.

HINT:

If the engine coolant temperature is 35°C or more, 5 hours after the power switch has been turned off, the ECM (included in the hybrid vehicle control ECU) will begin performing a monitor check after another 2 hours. If the engine coolant temperature is still 35°C or more, 7 hours after the power switch has been turned off, the ECM will begin performing a monitor check after another 2.5 hours.

There are two methods for monitoring the EVAP system.

1. If the fuel tank pressure is higher or lower than the atmospheric pressure, the system determines that there are no leaks in the closed tank system and the system will check for leaks from the piping and canister between the purge VSV and canister pump module. (Method A)
2. If the fuel tank pressure is almost the same as the atmospheric pressure, vacuum will be allowed to enter the fuel tank and the system will check for leaks from the fuel tank after checking for leaks from the canister. (Method B)

Sequence	Operation	Description	Duration
-	ECM (Included in hybrid vehicle control ECU) activation	Activated by soak timer, 5 hours (7 or 9.5 hours) after power switch turned off.	-
A	Atmospheric pressure measurement	Vent valve turned OFF (vent) and EVAP system pressure is measured by ECM (included in the hybrid vehicle control ECU) in order to register atmospheric pressure. If pressure in EVAP system is not between 70 kPa and 110 kPa (525 mmHg and 825 mmHg), ECM (included in hybrid vehicle control ECU) cancels EVAP system monitor.	10 seconds
B	First 0.02 inch leak pressure measurement	In order to determine 0.02 inch leak pressure standard, vacuum pump creates negative pressure (vacuum) through 0.02 inch orifice and then ECM (included in the hybrid vehicle control ECU) checks if vacuum pump and vent valve operate normally.	60 seconds
C	EVAP system pressure measurement	Vent valve is turned ON (closed) to shut EVAP system. Negative pressure (vacuum) is created in EVAP system, and EVAP system pressure is then measured. Write down measured values as they will be used in leak check. If EVAP pressure does not stabilize within 15 minutes, ECM (included in hybrid vehicle control ECU) cancels EVAP system monitor.	15 minutes
D	Purge VSV monitor	Purge VSV opens and then EVAP system pressure is measured by ECM (included in hybrid vehicle control ECU). Large increase indicates normal.	10 seconds
E	Second 0.02 inch leak pressure measurement	After second 0.02 inch leak pressure measurement, leak check is performed by comparing first and second 0.02 inch leak pressure standards. If stabilized system pressure is higher than second 0.02 inch leak pressure standard, ECM (included in the hybrid vehicle control ECU) determines that EVAP system has a leak.	60 seconds
F	Resetting	Fuel tank pressure is compared with atmospheric pressure. If tank pressure is higher than PH or lower than PL, ECM (Included in hybrid vehicle control ECU) determines that EVAP system is normal and runs sequence I in method B. If tank pressure is around atmospheric pressure, ECM performs sequence G in method A.	5 seconds
G	Fuel tank pressure measurement	Vent valve is turned ON (closed). Fuel vapor-containment valve opens to allow negative pressure to enter the fuel tank and fuel tank pressure is measured. Write down measured values because they will be used in leak check. If fuel tank pressure does not stabilize within 15 minutes, ECM (included in the hybrid vehicle control ECU) stops monitoring.	15 seconds*
H	Third 0.02 inch leak pressure measurement	After 3rd 0.02 inch leak pressure measurement, leak check of fuel tank is performed. If recorded fuel tank pressure is higher than 3rd 0.02 inch leak pressure, ECM (included in the hybrid vehicle control ECU) determines that EVAP system has a leakage.	60 seconds
I	Fuel vapor-containment valve close stuck check	Fuel vapor-containment valve is opened for a certain period of time to check whether the valve is stuck closed.	0.1 second
J	Final check	Atmospheric pressure is measured and then monitoring result is recorded by ECM (included in the hybrid vehicle control ECU).	-
HINT: *: If there is only a small amount of fuel in the fuel tank, stabilizing the EVAP pressure takes longer than usual.

Purge flow monitor 

If EVAP system pressure change is less than 7.5 mmHg (1 kPa) when the engine is running and the purge VSV is turned ON (closed), the ECM (included in the hybrid vehicle control ECU) determines that the purge flow is insufficient.