VW_MKIV_Golf-Jetta_1.8T_EVAP_System_Servicing.pdf

Volkswagen Golf, GTI, Jetta 1999-2004, Jetta Wagon 2001-2004 - 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AWD, AWW, AWP

20-48

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Evaporative emissions system

Function description of EVAP canister system

Depending upon the air pressure and ambient

temperature, fuel vapor will form above the level of fuel

in the tank.

The Evaporative Emissions system prevents these HC

emissions escaping to the atmosphere.

Advanced

In limited quantities, fuel vapors pass through a gravity

valve (which closes at an angle of 45 ) located at the

highest point in the tank and through a pressure

retention valve into the evaporative emissions (EVAP)

canister.

Version: 2.5r01sp0003

The EVAP canister stores these vapors like a sponge.

Volkswagen Golf, GTI, Jetta 1999-2004, Jetta Wagon 2001-2004 - 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AWD, AWW, AWP

When the oxygen sensor control is active when driving

(engine warm), the EVAP canister purge regulator valve

-N80-, is activated (pulsed) from the engine control

module depending upon load and engine speed. The

opening period is dependent on the input signals.

Intake manifold vacuum draws fresh air through the vent

opening on the underside of the EVAP canister during

the purging procedure (regenerating the activated

charcoal in the canister). The fuel vapors stored in the

activated charcoal and fresh air are pulse-fed for

combustion.

Volkswagen Golf, GTI, Jetta 1999-2004, Jetta Wagon 2001-2004 - 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AWD, AWW, AWP

20-49

The pressure retention valve prevents fuel vapors from

being drawn from the tank when the solenoid valve is

open and intake manifold vacuum is present. It therefore

ensures that the evacuation of the EVAP canister has

priority.

No voltage (e.g. wiring open circuit) the solenoid valve is

closed and the EVAP canister will not be purged.

The vacuum line from the throttle valve control part to

the EVAP canister has an additional by-pass which is

connected with the cylinder block breather valve. The

non-return valve integrated in the cylinder block

breather valve prevents the intake air gassing into the

cylinder block during some partial load ranges. This

improves the overall cylinder block breathing. The by-

pass guarantees the cylinder block breathing.

Functional description of leak diagnosis

The evaporative emissions system (including fuel tank)

is equipped with a leak diagnosis, the leak diagnosis will

detect whether the system is leaking.

Volkswagen Golf, GTI, Jetta 1999-2004, Jetta Wagon 2001-2004 - 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AWD, AWW, AWP

The diagnosis operates by pressurizing the system and

should detect leaks where the damage exceeds 1 mm in

diameter.

During the diagnosis the Leak Detection Pump (LDP) -

V144- builds up a pressure of approx. 30 mbar in the

evaporative emissions system. The pump will switch off

when the pressure is attained. When the pressure falls

to below a certain figure, the pump will switch on again.

The On Board Diagnostic (OBD) monitors the time

between the switched on periods and if it is too short it

will register a code in the DTC memory.

Volkswagen Golf, GTI, Jetta 1999-2004, Jetta Wagon 2001-2004 - 1.8 Liter 4-Cyl. 5V Turbo Engine Mechanical, Engine Code(s): AWD, AWW, AWP

20-50

Note:

Hose connections are secured with either spring-

type or clamp-type clips.

Always replace clamp-type clips with spring-type

clips.

Assembly tool VAS 5024 or hose clip pliers V.A.G

1921 are recommended for installing spring-type

clips.

Observe safety precautions

Page 20-11 .

Observe rules for cleanliness

Page 20-13 .

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