1994 Audi S4FACTORY OEM SERVICE PROCEDURE

Board Computer Control For Boost Pressure Display Checking

NOTE: All voltage and continuity tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated differently in testing procedures. For help with diagnostic testing. See WIRING DIAGRAMS .

Perform the following check only if the boost pressure signal is absent or incorrect, as determined by the board computer check.

  1. Connect (VAG 1598) test box to ECM wiring harness using (VAG 1598/5) adaptor cable. See CONNECTING VAG 1598 TEST BOX . ECM is not connected.
  2. Using DVOM, switched to voltage range. Connect multimeter between terminal No. 19 (ground) and terminal No. 32.
  3. Run engine, and continuously vary Engine Speed (RPM) between 1000-4000 RPM.
  4. Voltage must fluctuate between 0.3 and 10.0 Volts (proportional to RPM).
  5. If YES (even though board computer does NOT display boost pressure value): Switch ignition OFF (stop engine).
  6. Remove instrument cluster for access to board computer.
  7. Check for continuity between ECM terminal No. 32 (test box terminal 31), and black 10-pin connector of board computer, see Figure. See WIRING DIAGRAMS . If wiring is Okay: Eliminate fault in instrument cluster.
  8. If specified voltage is NOT obtained: Switch OFF engine.
  9. Remove instrument cluster.
  10. Disconnect black 10-pin connector from board computer. Run engine: Must be 0.3-10.0 volts (will vary with boost pressure).
  11. If YES: Malfunction is in board computer. If NO: Check wiring for short to positive or ground between ECM and board computer 10-pin connector, using wiring diagram. See WIRING DIAGRAMS .
  12. If wiring is Okay: Replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.
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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.