Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Audi 100 Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Hall Effect Sending Unit
- Remove protective cover from Hall Effect sending unit (on distributor) and unplug 3-wire connector from unit. Connect voltmeter to connector terminals No. 1 and 3. Turn ignition on. Voltmeter reading should be 9 volts minimum.
- If reading is not as specified, check for open circuit in wiring between sending unit and ECU terminals No. 23 and 25. See Figure for ECU terminal identifications. If reading is as specified, turn ignition off. Move back connector cover to gain access to rear of 3-wire connector. Reinstall 3-wire connector to distributor Hall sending unit. Connect voltmeter between terminals No. 1 and 2 at rear of 3-wire connector.
- Remove distributor cap, rotor and dust cover. Turn crankshaft by hand until rotor window clears sending unit. Turn ignition on. Voltmeter should read minimum of 4 volts.
- Turn crankshaft until rotor window fully aligns with sending unit. Voltmeter should read 0-.5 volt. Turn ignition off. If readings are not as specified, replace Hall Effect sending unit. If readings are as specified, check wiring between Hall Effect sending unit and ECU for shorts or opens in wires and repair as necessary. If circuits are okay, replace ECU.
Factory Service Tools
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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.