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.
1989 Audi 90 Base, AutomaticFACTORY OEM SERVICE PROCEDURE
OXS Frequency Valve
- Disconnect harness connector from OXS frequency valve. Using a LED Test Light (US 1115), connect Red lead to terminal No. one and Black lead to terminal No. 2.
- Perform output code self-diagnosis as previously described. When code appears, LED test light must be off. If light is off, replace OXS frequency valve.
- If light came on, ensure 12 volts are present between oxygen sensor terminal No. 1 and ground. If necessary, repair wiring or circuits.
- If 12 volts are present, turn ignition off. Disconnect ECU harness connector. Check for about 10 ohms in wire between ECU terminal No. 8 and oxygen sensor terminal No. 2. See Figure . If ohms are not as specified, check for an open circuit in wire. If circuit is not open, replace ECU.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.