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
- engine coolant temperature 60°C (140°F) minimum
- do not take measurements during periods when radiator cooling is running





Potentiometer, checking

- disconnect harness connector from air flow sensor potentiometer
- connect VAG 1501 test adaptor between potentiometer (G 19) and potentiometer harness connector (arrows)
- switch Fluke 83 multimeter to 20 Volt range
- connect multimeter to adaptor wires 1 and 3 of VAG 1501 test adaptor using jumper wires from VW 1594 adaptor kit
- switch ON ignition
- must be 4.35 to 5.35 Volts.

- switch OFF ignition

- connect multimeter to adaptor wires 2 and 3 of VAG 1501 test adaptor
- start engine and let idle for 2 minutes minimum







- measure voltage and compare to chart.
- U1 = voltage measured between adaptor leads 1 and 3
- U2 = voltage between adaptor leads 2 and 3

If U2 voltage falls below tolerance limit

- check intake system for air leaks
- between air flow sensor and cylinder head
- between possibly damaged connector pipe and intake air boot/throttle body
- at carbon canister solenoid valve

If a leak is defected and U2 voltage exceeds tolerance slightly

- carefully remove sealing compound covering potentiometer trim screw.







- adjust U2 voltage using trim screw (arrow)
- try to obtain a nominal voltage with the shaded area of the chart

If an acceptable adjustment is not possible

- replace air flow sensor assembly

- Cover trim screw with a dab of silicon adhesive sealing compound