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
Engine Speed Sensors
- Remove Gray (engine RPM) and Black (ignition timing reference) connectors from bracket near ignition coil. For each connector, check continuity between terminals No. 1 and 2. See Fig 2 . Ohmmeter reading should be 1000 ohms.
- If not, replace sensor(s). If reading is correct, check continuity between terminals No. 1 and 3, and terminals No. 2 and 3 for each connector. If ohmmeter reading is not infinity (4), replace sensor(s).
- Unplug connector from ECU. Check wiring between harness side of each sensor connector and ECU. See Fig 1
and Fig 2
. Ensure resistance of each wire between ECU and sensor connectors is zero ohm. See ENGINE SPEED SENSOR CIRCUITS table.ENGINE SPEED SENSOR CIRCUITS
Sensor Terminal ECU Harness Connector Terminal Engine RPM (Gray) 1 29 2 11 3 28 Ignition Timing Reference (Black) 1 13 2 12 3 28 - Ensure clearance between ignition timing reference sensor and flywheel pin is .43" (1.10 mm). If engine speed sensors and wiring circuits are okay, replace control unit.
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.