Air Flow Sensor Potentiometer, Checking

CAUTION

The potentiometer is precisely adjusted at the factory after which the mounting screws are coated with sealant. Do NOT loosen for any reason!

Requirement
^ engine oil temperature 60~C (140~F) minimum





^ connect adaptor lead VAG 1501 between potentiometer and potentiometer harness connector
^ switch multimeter US 1119 to 20 volt range
^ connect multimeter to terminals 1 and 3 of VAG 1501 adaptor (to measure U, supply voltage)
^ switch ON ignition
^ must be 4.35 to 5.35 volts

If NO

^ check wiring and connectors between control unit and potentiometer, using wiring diagram, repair as necessary

If wiring OK

^ replace control unit (J 204)

If voltage U1 OK

^ switch OFF ignition
^ connect multimeter between terminals 2 and 3 of adaptor VAG 1501 (to measure U2 resulting voltage)





^ start engine and let idle
^ displayed voltage must fall within shaded area of chart


CAUTION

Radiator cooling fan must NOT be running while taking these measurements.

If U2 voltage lies slightly out of tolerance

^ check for air leaks
^ possibility of incorrectly installed throttle body gasket

^ repair as necessary

If NO air leaks





^ remove sealing compound covering potentiometer trim screw (arrow)
^ rotate trim screw as necessary to achieve a value that falls within the chart
^ after adjusting, seal head of trim screw with silicone seater

If an acceptable adjustment is NOT obtained

^ replace airflow sensor assembly complete with potentiometer