Passat L4-1984cc 2.0L DOHC (9A) (1990)
Air Flow Meter/Sensor: Testing and Inspection
Air Flow Sensor Potentiometer, Checking and Adjusting
NOTE: The potentiometer is precisely adjusted at the factory; to prevent tampering and/or adjustments the trim and mounting screws are then
covered with sealing compound.
Requirements
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engine coolant temperature 60°C (140°F) minimum
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do not take measurements during periods when radiator cooling is running
Potentiometer, checking
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disconnect harness connector from air flow sensor potentiometer
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connect VAG 1501 test adaptor between potentiometer (G 19) and potentiometer harness connector (arrows)
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switch Fluke 83 multimeter to 20 Volt range
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connect multimeter to adaptor wires 1 and 3 of VAG 1501 test adaptor using jumper wires from VW 1594 adaptor kit
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switch ON ignition
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must be 4.35 to 5.35 Volts.
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switch OFF ignition
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connect multimeter to adaptor wires 2 and 3 of VAG 1501 test adaptor
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start engine and let idle for 2 minutes minimum
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measure voltage and compare to chart.
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U1 = voltage measured between adaptor leads 1 and 3
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U2 = voltage between adaptor leads 2 and 3
If U2 voltage falls below tolerance limit
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check intake system for air leaks
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between air flow sensor and cylinder head
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between possibly damaged connector pipe and intake air boot/throttle body
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at carbon canister solenoid valve
If a leak is defected and U2 voltage exceeds tolerance slightly
-
carefully remove sealing compound covering potentiometer trim screw.