Testing the fuel cap

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Remove fuel cap.

Fig 1: Testing The Fuel Cap

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Connect fuel cap receiver - arrow - to hose.
Screw fuel cap tightly to cap receiver.
Turn control valve to "Test" pressurizing cap.
Turn valve to "Hold".

Watch pressure gauge for drop in pressure from 14 inches H ₂ O.

If no pressure drop is indicated:

Proceed to Checking Leak Detection Pump V144 for internal leaks.

If pressure drop is indicated:

Replace fuel cap and re-test.
Proceed to Checking Leak Detection Pump V144 for internal leaks.