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
Fuel Pump Relay
- With ignition off, remove fuel pump relay from relay panel. Connect multimeter between relay terminals No. 48 and 50. See Fig 1 . Multimeter should read 12 volts.
- Connect multimeter between terminals No. 46 and 50. Turn ignition on. Multimeter should read 12 volts.
- If multimeter does not read as specified, repair break in wiring. Connect multimeter between terminals No. 46 and 47. Momentarily engage starter. Multimeter should read 7 volts.NOTE: ICU terminal identifications are located on connector.
- If multimeter does not read 7 volts, partially remove ICU and disconnect harness connector. Using a multimeter, check continuity between ICU and fuel pump relay.
- Connect ICU connector terminal No. 3 to relay terminal No. 49. Connect ICU connector terminal No. 14 and relay terminal No. 47. Multimeter reading should be .2 ohm.
- If reading is not as specified, repair break in wiring. If reading is as specified, replace knock sensor.
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.