Checking EVAP system for leaks

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Fig 1: Identifying Leak Detection Pump (LDP) Outlet Hose (EVAP side)

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Clamp off LDP outlet (EVAP side) - 1 - using Hose Clamps up to 25 mm dia. 3094 or equivalent.

CAUTION: Clamp only soft rubber lines when isolating a leak. To avoid risk of damage, never clamp hard plastic lines!

Turn control valve from "Hold" to "Test".
Allow fuel system to pressurize.

NOTE:

Fuel system pressurization depends on volume of fuel system and amount of fuel in tank.

If fuel system pressurization does not stabilize:

Verify that all fuel system outlets have been sealed before continuing.

NOTE:

Any flow shown on flow meter indicates a leak. Flow below flow meter flag set at vehicle leak standard may indicate a sporadic DTC.

If flow meter on tester registers flow near or above pre-set pressure:

Clamp off hose leading from EVAP canister purge regulator valve N80 to intake manifold.

If flow stops:

Replace EVAP canister purge regulator valve N80 and repeat test before continuing.

If meter indicates no flow after test:

Perform quality check and return vehicle to customer.

If flow continues:

Use smoke generator trigger to charge fuel system with smoke again.
Inspect complete EVAP system for escaping smoke.

NOTE:

It may be necessary to move, twist, or wiggle EVAP components around to reproduce leak.

If leak cannot be found using smoke:

Fig 2: Identifying Ultrasonic Tester

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Locate leak with ultrasonic tester.

General search: tester only
Localized search: tester with extension wand (left)

If leak cannot be located:

Disconnect and plug or clamp shut EVAP lines to isolate fuel tank using Hose Clamps up to 25 mm dia. 3094 or equivalent before continuing.

CAUTION: Clamp only soft rubber lines when isolating a leak. To avoid risk of damage, never clamp hard plastic lines!

If flow stops:

Reconnect EVAP lines and search area that was isolated.

When leak has been located:

Repair leak and repeat EVAP system test.

NOTE:

Because leak may be at top of fuel tank, it may not be possible to locate through fuel pump/sending unit access plate.
Lower fuel tank if necessary to locate leak.

CAUTION: Do not return vehicle to the customer without having performed a proper diagnosis and repair.