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
Starting Enrichment
- Ensure engine is at normal operating temperature and no fault codes are stored in ECU memory. Using digital Multimeter (US 1119) and Adapter (VW 1315A/1), check voltage at differential pressure regulator.
- Using adapter, connect multimeter to differential pressure regulator. See Figure . Remove fuse No. 13 and ground ignition coil wire. Crank engine and observe current reading. Control current should drop to 35-45 mA during engine cranking, and should 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 Coolant Temperature Sensor (CTS) harness connectors. Connect Adjustable Resistance Box (VW 1630) leads to CTS harness connectors. Set resistance to 2500 ohms. Install ignition coil wire and start engine. Control current should read 15-23 mA in about 6-9 seconds, then slowly drops to 9-11 mA.
- Move throttle quickly to full throttle and release. Control current should increase briefly to 6 mA. If system fails test, perform electrical tests. See Figure and CIS-MOTRONIC VOLTAGE & RESISTANCE TESTS table. If system electrical tests are okay, replace ECU and 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.