EVAP System: Description

While the engine is running, if a predetermined condition (closed loop, etc.) is met, the EVAP VSV is opened by the ECM (Included in HV 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 EVAP VSV to control purge flow volume. Purge flow volume is also determined by the intake manifold pressure. Atmospheric pressure is allowed into 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 EVAP that is 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.
EVAP VSV	Opens or closes line between canister and intake manifold. ECM (Included in HV control ECU) opens and closes EVAP VSV to control EVAP purge flow. ECM opens purge valve to purge vapor gas that was 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 HV control ECU). To ensure that EVAP monitor values will be accurate, soak timer counts 5 hours (-15 minutes) from when ignition 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 closes to keep vapor in the tank and prevent it from being absorbed in canister. During refueling, valve opens and vapor is absorbed in canister. When driving, valve acts to change pressure in the tank slightly positive.
Fuel tank pressure sensor	Converts fuel tank pressure into voltage and outputs that voltage. ECM (Included in HV control ECU) supplies a constant voltage of 5 V to pressure sensor and uses feedback from sensor to monitor fuel tank pressure, (fig. 3)
Pump module	(a) to (e) below are pump module components. Pump module cannot be disassembled.
(a) Vent valve	Vents and closes EVAP system. When ECM (Included in HV control ECU) turns valve ON, EVAP system is closed. When, ECM turns valve OFF, EVAP system is vented, negative pressure (vacuum) is created in EVAP system to check EVAP leaks by closing EVAP VSV, turning on vent valve (closed) and operating vacuum pump (refer to Fig 3).
(b) Pressure sensor	Indicates EVAP pressure as voltage 5 V is applied by ECM (Included in HV control ECU). ECM detects EVAP system pressure using this voltage (refer to Fig 4).
(c) Check valve	Composed of nylon ball and spring. Valve blocks off atmosphere from the vacuum pump.
(d) Vacuum pump	Negative pressure (vacuum) is created in EVAP system for leak check.
(e) 0.02 inch orifice	Negative pressure (vacuum) is created in 0.02 inch orifice to measure "0.02 inch leak pressure" by closing EVAP VSV, turning off vent valve (vent) and operating vacuum pump. "0.02 inch leak pressure" indicates criterion of EVAP small leak.

Key-off monitor 

This monitoring system checks for 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 ignition switch has been turned off, the ECM (Included in HV 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 ignition 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 EVAP VSV and pump module. (Method A)
2. If the fuel tank pressure is almost the same as the atmospheric pressure, vacuum pressure will 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 HV control ECU) activation	Activated by soak timer, 5 hours (7 or 9.5 hours) after ignition switch turned off.	-
A	Atmospheric pressure measurement	Vent valve turned OFF (vent) and EVAP system pressure is measured by ECM (Included in HV 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 HV 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 HV 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 HV control ECU) cancels EVAP system monitor.	15 minutes
D	EVAP VSV monitor	EVAP VSV opens and then EVAP system pressure is measured by ECM (included in HV 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 HV control ECU) determines that EVAP system has a leakage.	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 HV 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 into 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 HV 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 HV 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 HV 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 EVAP VSV is turned ON (closed), the ECM (Included in HV control ECU) determines that the purge flow is insufficient.