Toyota Evap Purge Valve Duty Cycle

NOTICE:

The canister is located near the fuel tank, underneath the body.

2004 Toyota Tacoma Evap System

NOTICE:

In this vehicle's EVAP system, turning ON the vent valve does not seal off the EVAP system. To check for leaks in the EVAP system, disconnect the air inlet vent hose and apply pressure from the atmosphere side of the canister.

While the engine is running, if a predetermined condition (closed-loop etc.) is met, the purge VSV is opened by the ECM and stored fuel vapors in the canister are purged to the intake manifold. The ECM changes the duty cycle ratio of the purge VSV to control purge flow volume. The 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 the purge flow is maintained when the negative pressure (vacuum) is applied to the canister.

The following two monitors run to confirm appropriate EVAP system operation.

1. Key-off monitor

This monitor checks for EVAP (Evaporative Emission) system leaks and canister pump module

malfunctions. The monitor starts 5 hours after the ignition switch is turned OFF. More than 5 hours are required to allow enough time for the fuel to cool down to stabilize the fuel tank pressure, thus making the EVAP system monitor more accurate.

The electric leak detection pump creates negative pressure (vacuum) in the EVAP system and the pressure is measured. Finally, the ECM monitors for leaks from the EVAP system, and malfunctions in both the canister pump module and purge VSV, based on the EVAP pressure.

HINT:

: If the engine coolant temperature is not below 35°C (95°F) 5 hours after the ignition switch is turned 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 the two monitors. The 1st monitor is always conducted every time and the 2nd monitor is activated if necessary.

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 vent valve is turned OFF (open) and the EVAP pressure is then measured. If the variation in the pressure is less than 0.5 kPa (3.75 mmHg), 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.

EVAP Purge Flow:

Reference Orifice (0.02 inch)

Fuel Cap

Refueling Valve n

Purge VSV (ON)

To Intake Manifold

Reference Orifice (0.02 inch)

Fuel Cap

Refueling Valve

Evap Purge Flow Monitor

Canister Filter Leak Detection Pump (OFF)

Soak Timer

Vent Valve (OFF) Canister Pump Module

Components

Operations

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, Close: 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. When valve open, adding fuel into fuel tank possible.

Roll-over valve

Located in fuel tank. Valve closes 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 fuel tank pressure. When approx 5 hours elapsed, ECM activates (refer to fig. 3).

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. 1).

(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. 2).

(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 0.02 inch leak criterion. 0.02 inch leak criterion indicates small leak of EVAP.

Canister Pump Module (fig. 1):

: Airflow

Condition: Purge Flow

Condition: Leak Check

Vent Valve: OFF (vent)

Reference Orifice

Canister Pressure Sensor

Condition: Purge Flow

Reference Orifice

From Refueling Valve

Leak Detection Pump: OFF

To Canister Filter

-(Atmosphere)

From Refueling Valve

Leak Detection Pump: OFF

Vent Valve: ON (closed)

To Canister Filter

-(Atmosphere)

Leak Detection Pump: ON

A115902E01

Canister Pressure Sensor Specification (fig. 2):

HINT:

Standard atmospheric pressure is 101.3 kPa (760 mmHg)

Soak Timer Circuit (fig.3)

Ignition Switch

Battry

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Responses

  • walter
    What does the purge valve do in a tacoma truck?
    5 months ago
  • alfred
    How to change evap valve on 2006 tacoma?
    2 months ago
  • abel
    Where is the evap canister on a 2010 tacoma located?
    1 month ago

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