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.
1991 Audi 100 BaseFACTORY OEM SERVICE PROCEDURE
Oxygen (O2) Sensor Control (2.8L)
- Disconnect oxygen sensor connector. See COMPONENT LOCATIONS . Measure resistance between engine ground and oxygen sensor connector terminal (component side of connector). If resistance is not infinite, replace oxygen sensor.
- If resistance is infinite, set voltmeter on 2 volt DC scale. Turn ignition on. Measure voltage between engine ground and oxygen sensor connector terminal (component side of connector). If 350-450 millivolts are present, oxygen sensor is okay. If 350-450 millivolts are not present, check wiring. If wiring is 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.