1987 Volkswagen Quantum Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Electrical Testing

NOTE: ECU is located near glove box.
  1. Locate ECU and press locking tabs back to disconnect connector. All connectors are wired with pin numbers in same location. Use volt-ohmmeter for testing.
  2. Refer to wiring diagram for pin locations. With fuel pump relay jumper wire in place, turn ignition on and check for battery voltage at terminals No. 8 and 15 (18 and 1 on Jetta). Connect ground lead of voltmeter to terminals No. 5 and 16 (2, 10 and 22 on Jetta) while checking for battery voltage to ensure these wires make good ground connection.
  3. If battery voltage is not available at terminal No. 8 or 18, check Lambda and fuel pump relays. If there is no voltage at terminal No. 15 or 1, check frequency valve connector. One wire should have battery voltage and other wire should have continuity to terminal No. 15 or 1. Frequency valve should have 2-3 ohms resistance. Repair or replace as necessary.
  4. Disconnect oxygen sensor and check for continuity between sensor lead and terminal No. 2 (11 on Jetta). No continuity should exist between ground and lead wire.
  5. All models use switches for enrichment signal. All switches provide continuity to ground when switch is closed. Actuate throttle to test throttle valve switches.
  6. Thermal switches can be checked by removing switch and heating in water. Repair wiring or replace switches as necessary.
  7. After testing is completed, reconnect ECU, oxygen sensor and all switches. Remove fuel pump relay jumper wire and testing equipment.
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.

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