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
Starting Enrichment
- Ensure engine is at normal operating temperature and no fault codes are stored in ECU memory. Using a digital multimeter and Harness Adapter (VW1315A/1), check voltage at differential pressure regulator.
- Connect multimeter to differential pressure regulator. See Figure . Remove fuse No. 13 and remove and ground ignition coil wire. Crank engine and observe volt reading. Control voltage should drop to 35-45 mA, during engine cranking, and remain there for a maximum of 3 seconds. After 3 seconds, voltage should drop to zero.
- With multimeter still connected and ignition off, disconnect O2 sensor and CTS harness connectors. Connect Adjustable Resistance Box (VW1630) leads to CTS harness connectors. Set resistance to 2500 ohms. Install ignition coil wire and start engine. Control voltage should read 15-23mA in about 6-9 seconds, then slowly drop to 9-11 mA.
- Move throttle quickly to full throttle and release throttle. Control voltage must increase briefly to 6 mA. If system fails test, perform electrical tests. See CIS-MOTRONIC VOLTAGE & RESISTANCE TESTS chart. See Figure . If system electrical tests are okay, replace ECU. Clear fault codes.
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.