Toyota Tundra. Manual — part 1439

off, the monitor check starts 2 hours later. If it is still not below 35°C (95°F) 7 hours after the ignition
switch is turned off, the monitor check starts 2.5 hours later.

2. Purge flow monitor

The purge flow monitor consists of 2 monitors. The 1st monitor is conducted every time and the 2nd
monitor is activated if necessary.



The 1st monitor

While the engine is running and the purge VSV (Vacuum Switching Valve) is ON (open), the ECM
monitors the purge flow by measuring the EVAP pressure change. If negative pressure is not
created, the ECM begins the 2nd monitor.



The 2nd monitor

The vent valve is turned OFF (open) and the EVAP pressure is measured. If the variation in the
pressure is less than 0.5 kPa-g (3.75 mmHg-g), the ECM interprets this as the purge VSV being
stuck closed, and illuminates the MIL and sets DTC P0441 (2 trip detection logic).

Atmospheric pressure check:

In order to ensure reliable malfunction detection, the variation between the atmospheric pressures, before and
after conduction of the purge flow monitor, is measured by the ECM.

Fig. 247: EVAP Purge Flow Diagram

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

COMPONENTS OPERATION

Component

Operation

Canister

Contains activated charcoal to absorb EVAP (Evaporative Emissions) generated in
fuel tank.

Cut-off valve

Located in fuel tank. Valve floats and closes when fuel tank 100% full.

Purge VSV
(Vacuum
Switching Valve)

Opens or closes line between canister and intake manifold. ECM uses purge VSV to
control EVAP purge flow. In order to discharge EVAP absorbed by canister to intake
manifold, ECM opens purge VSV. EVAP discharge volume to intake manifold
controlled by purge VSV duty cycle ratio (current-carrying time) (Open: ON; Closed:
OFF).

Refueling valve

Controls EVAP pressure from fuel tank to canister. Valve consists of diaphragm,
spring and restrictor (diameter: 0.08 inch). When fuel vapor and pressure inside fuel
tank increase, valve opens. While EVAP purged, valve closes and restrictor prevents
large amount of vacuum from affecting pressure in fuel tank. Valve opened while
refueling.

Roll-over valve

Located in fuel tank. Valve closed by its own weight when vehicle overturns to
prevent fuel from spilling out.

Soak timer

Built into ECM. To ensure accurate EVAP monitor, measures 5 hours (+/-15 min)
after ignition switch turned off. This allows fuel to cool down, stabilizing EVAP
pressure. When approximately 5 hours elapsed, ECM activates (refer to Fig. 250).

Canister pump
module

Consists of (a) to (d) below. Canister pump module cannot be disassembled.

(a) Vent valve

Vents and closes EVAP system. When ECM turns valve ON, EVAP system closed.
When ECM turns valve OFF, EVAP system vented. Negative pressure (vacuum)
created in EVAP system to check for EVAP leaks by closing purge VSV, turning on
vent valve (closed) and operating leak detection pump (refer to Fig. 248).

(b) Canister
pressure sensor

Indicates pressure as voltages. ECM supplies regulated 5 V to canister pressure sensor,
and uses feedback from sensor to monitor EVAP system pressure (refer to Fig. 249).

(c) Leak detection
pump

Creates negative pressure (vacuum) in EVAP system for leak check.

(d) Reference
orifice

Has opening with 0.02 inch diameter. Vacuum produced through orifice by closing
purge VSV, turning off vent valve and operating leak detection pump, to monitor
reference pressure. Reference pressure indicates small leak of EVAP.

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

Fig. 248: Canister Pump Module Air Flow Diagram

Fig. 249: Canister Pressure Sensor Specification Ouput Voltage Graph

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra

Fig. 250: Soak Timer Circuit Diagram

WIRING DIAGRAM

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (2UZ-FE) - Tundra