80 L4-1984cc 2.0L SOHC (3A) (1989)
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disconnect potentiometer harness connector and connect VW 1501 test adaptor between potentiometer and harness connector
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switch multimeter US 1119 to 20 volt range and connect to terminals 1 and 3 (U, voltage) of VW 1501 adaptor
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switch ON ignition
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must be 4.35 to 5.35 volts
If NO
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check wiring between Motronic control unit and potentiometer using wiring diagram, repair as necessary
If wiring OK
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replace Motronic control unit
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switch multimeter US 1119 to 2 volt range and connect to terminals 2 and 3 (U2 voltage) of VW 1501 adaptor
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switch ON ignition (but do NOT start engine)
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U2 voltage must fall within shaded area of graph
If NO
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remove sealing compound covering head of potentiometer trim screw
CAUTION
Do NOT damage the trim screw when scraping away the sealing compound.
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adjust U2 voltage via trim screw (arrow), while observing multimeter, until required voltage is obtained
