1991 Audi 100 BaseFACTORY OEM SERVICE PROCEDURE

Hall Effect Sending Unit

  1. Remove protective cover from Hall Effect sending unit (on distributor) and unplug connector. Connect voltmeter to harness connector terminals No. 1 (negative) and No.3 (Red/Black wire).
  2. Turn ignition on. Voltmeter reading should be greater than 9 volts. If reading is not as specified, check for open circuit in wiring between ECU terminals No. 23 and No. 25, and Hall Effect sending unit. See Figure for ECU terminal identification.
  3. If reading is as specified, turn ignition off. Move connector cover to access rear of 3-wire connector. Install connector to distributor Hall Effect sending unit. Connect voltmeter between terminals No. 1 (negative) and No. 2 (Green wire) at rear of connector.
  4. Remove distributor cap, rotor and dust cover. Turn crankshaft by hand until rotor window is clear of sending unit. Turn ignition on. Voltmeter should indicate minimum of 4 volts.
  5. Turn crankshaft until rotor window fully aligns with sending unit. Voltmeter should indicate 0-.5 volt. Turn ignition off. If readings are not as specified, replace Hall Effect sending unit.
  6. If readings are as specified, check wiring between Hall Effect sending unit and ECU for short or open circuits. Repair wires if necessary. If circuits are okay, replace ECU.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.